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The drawings contained in this Recommendation have been done in Autocad
Recommendation T.100
INTERNATIONAL INFORMATION EXCHANGE FOR INTERACTIVE VIDEOTEX
(Geneva, 1980; amended at Malaga-Torremolinos, 1984)
CONTENTS
Preamble
1 Purpose and scope of this Recommendation
2 General Videotex coding structure
3 Common features
4 Representation of alphanumeric characters in a Videotex system
5 Alphamosaic option
6 Alphageometric option
7 Dynamically redefinable character sets (DRCS) option
8 Alphaphotographic option
9 Service enhancements
10 Line and end-to-end protocols
11 Interworking with other services
Annex A - The extension scheme of ISO 2022
Annex B - Repertoire of graphic characters
Preamble
The CCITT,
considering
(a) that there is increasing interest in public network-based new
interactive information retrieval services using domestic television receivers
suitably supplemented, or other apparatus, as terminal equipment;
(b) that the CCIR is studying standards for broadcast Teletext services for
general reception and has expressed a view that it is desirable that terminal
equipment compatibility should exist between broadcast Teletext systems for
general reception and public network-based data bank systems;
(c) that such services should be provided over public networks in
accordance with CCITT Recommendations and may be required to operate as an
international service;
(d) that such services may interwork with terminals provided for text
communication services (Teletex for example);
(e) that some Administrations intend to have an early introduction of, or
have introduced, public interactive Videotex
services;
unanimously recommends
that the following technical provisions be applied for international
information exchange for interactive Videotex service.
Fascicle VII.5 - Rec. T.100 PAGE1
1 Purpose and scope of the Recommendation
1.1 Purpose
1.1.1 The purpose of this Recommendation is:
a) to facilitate an orderly introduction of early Videotex services (including the continuation of existing
services, with a clear identification of potential
enhancements) that need to be considered in future
developments;
b) to identify parameters needed to design Videotex terminals; and
c) to provide technical recommendations desirable for
potential interworking of other services with Videotex
services.
1.2 Scope
1.2.1 This Recommendation describes the characteristics of coded information
that is exchanged between countries participating in the international
interactive Videotex service (as described in Recommendation F.300) and defines
the display features corresponding to its various elements.
1.2.2 Videotex systems are text communication systems having in addition the
capability of a given level of pictorial representation and a repertoire of
display attributes. The text and the pictures obtained are intended to be
displayed using the current television (TV) raster standards of the different
countries.
1.2.3 Different options are offered as a choice for the Administrations to
implement their national services. Substantial degrees of compatibility exist
between these options, but some transcoding may be necessary to facilitate
interworking.
1.2.4 For the international service, four different options for representing
pictorial information have been recognized:
a) mosaic character sets;
b) geometric system;
c) dynamically redefinable character sets;
d) photographic representation.
These options are not mutually exclusive and it is possible that systems
may develop using two or more options.
1.2.5 For international interworking, two categories of TV systems have to be
considered:
a) systems having a vertical resolution of 525 lines per TV frame at 30 TV
frames per second;
b) systems having a vertical resolution of 625 lines per TV frame at 25 TV
frames per second.
1.2.6 Interworking problems at the pictorial level between countries having
different recognized pictorial systems and/or television standards require
further study.
1.2.7 This Recommendation is structured as follows:
SS 1, 2 and 3 deal with the features common to all the options;
S 4 deals with the coding of characters of the Videotex alphanumeric
repertoire defined in Annex B;
S 5 deals with the alphamosaic option;
S 6 deals with the alphageometric option;
S 7 deals with the dynamically redefinable character sets (DRCS) option;
S 8 deals with the alphaphotographic option;
S 9 deals with future enhancements and identifies features requiring
further study such as: audio, downloaded software, motion, etc.;
S 10 deals with line and end-to-end protocols;
S 11 deals with interworking with other services.
Some of these parts have not been completed, and therefore contain
guidelines towards future extensions rather than a complete technical
specification.
2 General Videotex coding structure
2.1 General
2.1.1 The basis of the coding structure for the Videotex service is
Recommendation T.50 and the international standards ISO 2022, ISO 6937 for the
7-bit environment. Specifically, the shift-in code SI (0/15) invokes the G0 set
for alphanu text mode of operation, and the
shift-out code SO (0/14) invokes the G1 set, for all the models
(see Annex A). The use of the 8-bit coding scheme is for further
PAGE40 Fascicle VII.5 - Rec. T.100
study.
2.1.2 In addition to the provisions made by ISO 2022, the
transmission of alphabetic characters having diacritical signs is
effected by transmitting the code representing the diacritical mark
together with the code of the basic alphabetic character.
2.1.3 The different options are designated (and invoked) by specific
escape sequences.
2.2 Designation and invocation in the context of the alphamosaic option
2.2.1 Two differ the alphamosaic option have
been identified. They differ in their display control sets. These
control sets are designated as the C1 set by the following control
sequences: ESC 2/2 4/0 for the serial mode and ESC 2/2 4/1 for the
parallel mode, as assigned by ISO. Individual controls are
represented by: ESC Fe sequences.
2.2.2 The mosaic graphics set is designated (in the parallel mode)
as the G1 set by an escape sequence ESC 2/9 6/3 as allocated by
ISO.
2.3 Designation and invocation in the context of the alphageometric option
2.3. alphageometric coding scheme is to be
designated and invoked by the escape sequence ESC 2/5 (5/x) in
accordance with S 5.3.8 of ISO 2022 standard. This designates and
invokes a complete code with interpretation as follows.
2.3.2 All the meanings and interpretation of Recommendation T.50 and
ISO 2022 remain the same, including C0, G0 and G2 with the
exception of SI and SO. The codes of the G1 set and their meanings
and interpretations are as described in S 6.
2.3.3 The designation and invocation of the complete code by the
sequence ESC 2/5 (5/x) is to be terminated only by ESC 2/9 (F) or
ESC 2/13 (F), designating a normal G1 set.
2.4 Designation and invocation in the context of DRCS
2.4.1 A DRCS is a set of characters whose shapes are sent from the service and
down-loaded via the line. It may be used to represent alphabetic characters,
special symbols, or picture element symbols for constructing fine graphics. Once
loaded, the DRCS are regarded as members of a library that can be designated by
appropriate ESC sequences as G0, G1, G2, G3 sets. One scheme is described in S 7
in the context of a general architecture.
2.5 Designation and invocation in the context of the alphaphotographic option
(For further study.)
3 Common features
3.1 General
3.1.1 The features pertaining to individual systems will be described in the
corresponding paragraphs. The common features comprise common display features
and common control functions.
Fascicle VII.5 - Rec. T.100 PAGE1
3.2 Common display features
3.2.1 The defined display area is that rectangular position o
display in which all text and pictorial images may be presented
(see Figure 1/T.100).
3.2.2 The border area is that part of the visible display of a
terminal that is outside the defined display area (see Figure
1/T.100).
Fig. 1/T.100/CCITT-44080 = 6 cm
3.3 Common format effector and code extension control functions
3.3.1 General
3.3.1.1 The format effector control functions described for the Videotex system
permit the active drawing position to be moved on the visible display area. These
are taken from the C0 set (see Figure 2/T.100) together with the Space character
2/0. In order to permit interworking between Videotex and other text
communications services, these control functions have functional compatibility to
the extent possible with the basic C0 control set utilized by these other
services.
3.3.2 Format effector controls
3.3.2.1 Some of the format effector control functions may be used from terminal
to computer with different meanings.
3.3.2.2 Active position backward (APB)
This control function causes the active position to be moved one character
position backwards on the same row. APB on the first character position on the
row moves the active position to the last character position of the preceding
row. APB on the first character position on the first row moves the active
position to the last character position of the last row.
3.3.2.3 Active position forward (APF)
This function causes the active position to be moved to the next character
position forward on the same row. At the last position on the row, this control
moves the active position to the first character position on the following row.
APF on the last character position of the last row moves the active position to
the first character position of the first row.
3.3.2.4 Active position down (APD)
This function causes the active position to be moved to the equivalent
character position on the following row. APD on the last row moves the active
position of the equivalent character position of the first row of the display
frame or causes a roll-up to be made.
Fig. 2/T.100/CCITT-44090 = 25 cm
PAGE40 Fascicle VII.5 - Rec. T.100
3.3.2.5 Active position up (APU)
This function causes the active position to be moved to the equivalent
character position on the preceding row. APU on the first row moves the active
position to the equivalent character position on the last row of the same display
frame.
3.3.2.6 Clear screen (CS)
This function causes the screen to be cleared and causes the active
position to be moved to the first character position on the first row.
3.3.2.7 Active position return (APR)
This function causes the active position to be moved to the first
character position of the same row.
3.3.2.8 Space (SP)
A control function that causes the active position to be moved one
character width forward on the same row. It is also regarded as a graphic
character with no foreground. In those systems that define an explicit
background, the space copies the background colour into the active position and
moves the active position one character width forward. If used in conjunction
with the inversion attribute it copies the foreground colour into the active
position and moves the active position one character width forward.
3.3.2.9 Cancel (CAN)
A control function that fills all the character positions of the row,
after the active position, with spaces and returns the active position to its
original value.
3.3.3 Code extension control functions
3.3.3.1 Code extension control functions are used to expand the capability of
the 7-bit code beyond 128 different characters or functions. Code extension
functions alter the meaning of a number of characters following them.
3.3.3.2 Escape (ESC)
A control character that is used to provide additional control functions
other than transmission control functions and that alters the meaning of a
limited number of contiguously following bit combinations in the manner specified
in Recommendation T.51.
3.3.3.3 Control sequence introducer (CSI)
A code extension control function that is used to provide coded
representations for additional control functions, in particular for control
functions with parameters such as presentation control functions.
3.3.3.4 Shift-out (SO)
A control character that is used in conjunction with the Shift-in
character to extend the graphic character set of the code and that alters the
meaning of the bit combinations of columns 2-7 of the code table, until the
occurrence of the shift-in character, except that the meaning of the bit
combinations corresponding to the space character and the delete character
(positions 2/0 and 7/15) are unaffected.
3.3.3.5 Shift-in (SI)
A control character, used in conjunction with the shift-out character,
that reinstates the former meanings of the bit combinations of columns 2-7 of the
code table.
3.3.3.6 Single shift (SS2)
This character alters the meaning of the single-bit combination following
it. That bit combination must be one of those from columns 2-7 except 2/0 and
7/15. The meaning of the bit combination concerned is derived from an
appropriately designated G2 graphic set.
3.3.3.7 Single shift (SS3)
This character alters the meaning of the single-bit combination following
it. That bit combination must be one of those from columns 2-7 except 2/0 and
7/15. The meaning of the bit combination concerned is derived from an
appropriately designated G3 graphic set.
3.4 Miscellaneous
3.4.1 Null (NUL)
This function may occur in non-transparent modes in the received bit
stream at the terminal. It shall be regarded as a time filler and discarded.
3.4.2 Enquiry (ENQ)
A control character used as a request for a response from a remote
station, which response may include station identification and/or station status.
3.5 Coding of control functions
Fascicle VII.5 - Rec. T.100 PAGE1
3.5.1 A proposed coding of the control functions described is shown in Figure
2/T.100 as a C0 set, except for CSI which is coded in the C1 set.
4 Representation of alphanumeric characters in a Videotex system
4.1 General
4.1.1 The repertoire for the Latin alphabet is shown in Annex B. The repertoire
is derived from ISO 6937. Terminals capable of displaying a subset of the
Videotex repertoire shall be permitted.
4.1.2 Cha repertoires for non-latin based
languages can be accommodated in a similar manner to the latin
alphabet. (For further study.)
4.2 Coding
4.2.1 Section 4.2 describes the coding of characters the shape of which are
stored in the terminal. Some languages require that consecutive letters or
diacritical marks will be joined and that no space appear between the characters.
When an intersymbol space is required, it will be part of the character
description.
4.2.2 The code tables are shown in Figures 3/T.100 and 4/T.100. The code
combinations representing characters not included in the Videotex repertoire
shall not be transmitted.
F
F.300.
4.2.4 The graphic characters from columns 2, 3, 5, 6 and 7 of the supplementary
set are invoked one at a time by SS2.
4.2.5 A character with a diacritical mark is transmitted by the sequence SS2, a
character from column 4 from the supplementary set, and the appropriate character
from the primary set. The diacritical marks are nonVspacing.
4.2.6 The ISO registration of graphics character sets will indicate any special
features such as their use in conjunction with other graphic character sets or
nonVspacing characters, etc.
4.2.7 For languages based on other than the Latin alphabet further study is
required.
5 Alphamosaic option
5.1 General
5.1.1 In the alphamosaic option, the display frame is composed of defined
character positions which may be occupied by any of the characters of the
repertoire. The repertoire is composed of the alphanumeric repertoire and a
mosaic repertoire. The mosaic repertoire is formed by dividing the character
space into a matrix of 2 W 3 elements. There are 63 different combinations of
these elements.
PAGE40 Fascicle VII.5 - Rec. T.100
Fig. 3/T.100/CCITT-44100 = 25 cm
Fig. 4/T.100/CCITT-44111 = 25 cm
5.1.2 Two modes have been identified, which are known as serial and parallel
modes respectively. The two modes are distinguished by their display control sets
which are coded in C1 sets, designated and represented by ESC Fe sequences as
described in S 2.2.1.
5.1.3 The two modes have common features and specific features described in SS
5.2 to 5.4 below.
5.2 Common control functions
5.2.1 General functions
The active position home (APH)
This function causes the active position to be moved to the first position
of the first row. Its coded representation is 1/14 in Figure 2/T.100.
5.2.2 Device control functions
The following device control functions have been defined.
5.2.2.1 Definitions
cursor on (CON)
F: curseur en marche (CON)
S: cursor activo (CON)
The cursor on (CON) causes the active position to be visualized as a
marker.
cursor off (COF)
F: curseur arrêté (COF)
S: cursor inactivo (COF)
The cursor off (COF) causes the active position to be displayed in the
same way as other character positions.
device stop (DSP)
F: arrêt dispositif (DSP)
S: detención de dispositivo (DSP)
The device stop (DSP) causes a designated terminal device to stop.
device start (DST)
F: mise en marche dispositif (DST)
S: arranque de dispositivo (DST)
The device start (DST) causes a designated terminal device to start.
device wait (DW)
F: dispositif en attente (DW)
S: espera de dispositivo (DW)
The device wait (DW) causes a designated terminal device to pause.
5.2.2.2 Coding
CON is coded 1/1, COF is coded 1/4 in the C0 set. DSP, DST and DW
functions are coded as 3-character sequences of the Form ESC 3/x (P), where x =
7, 6 and 5 respectively, and P is a parameter that designates a particular
device.
5.3 Serial mode
5.3.1 General
5.3.1.1 The serial mode is based on the assumption that changes in character
attributes normally occur in interword spacings. This results in control
characters being serially stored in the page memory and normally results in their
display on the screen as a rectangle in the prevailing background colour.
5.3.1.2 The C1 set for the serial mode is given in Figure 5/T.100. Display
controls of the serial set causes the active position to be moved one character
position forward. In that case, the position thus vacated is to be generally
displayed as a space. The display control hold mosaics ESC 5/14 may modify this
situation.
5.3.2 Display control functions
5.3.2.1 The (Fe) codes are listed as follows:
5.3.2.2 Alpha red ü
Alpha green ï
Alpha yellow ï Controls functions that cause the currently
designated and invoked alphanumeric
Alpha blue ì set to be displayed in the indicated colour until
the occurrence of an explicit colour
Alpha magenta ï control or the end of a row.
Fascicle VII.5 - Rec. T.100 PAGE1
Alpha cyan ï
Alpha white Φ
Controls functions that cause the currently designated and invoked alphanumeric
set to be displayed in the indicated colour until the occurrence of an explicit
colour control or the end of a row.
5.3.2.3 Flashing
A control function that causes the characters following it in the same row
to be displayed alternately as they would normally be displayed, and as spaces,
in the prevailing background colour, under the control of a timing device in the
receiver.
5.3.2.4 Steady
A control function that causes the action of flashing to be stopped.
5.3.2.5 Start box
Reserved for starting the action of defining a picture area in a page of
text. (For further study.)
5.3.2.6 End box
Reserved for terminating the action of boxing. (For further study.)
5.3.2.7 Normal height
A control function that causes the graphic characters following it to
occupy one character position each.
5.3.2.8 Double height
A control function that causes the characters following it to occupy each
its active positive and the corresponding position on the following row.
5.3.2.9 Mosaics red ü
Mosaics green ï Control functions that cause the mosaic
graphic set to be displayed in the
Mosaics yellow ï indicated colour until the occurrence of an
explicit colour control or the
Mosaics blue ì end of the row. Unallocated code table
positions (4/0-5/15) cause the
Mosaics magenta ï characters of the currently designated and invoked
alphanumeric set to
Mosaics cyan ï be displayed. This is defined as
blast-through operation.
Mosaics white Φ
PAGE40 Fascicle VII.5 - Rec. T.100
Fig. 5/T.100/CCITT-44120 = 25 cm
Fascicle VII.5 - Rec. T.100 PAGE1
5.3.2.10 Conceal display
A control function that causes all characters following it, although
stored in the receiver, to be displayed as spaces until the user chooses to
reveal them.
5.3.2.11 Contiguous mosaics
A control function that causes the mosaic set to be displayed as
represented in Figure 6/T.100 with all cells being contiguous.
5.3.2.12 Separated mosaics
A control function that causes the mosaics set to be displayed as
represented in Figure 6/T.100 with all cells being separated by the prevailing
background colour.
5.3.2.13 Black background
A control function that causes the background colour to be black.
5.3.2.14 New background
A control function that causes the current colour as defined by previous
colour control functions to become the new background colour. The foreground
colour is unchanged.
5.3.2.15 Hold mosaics
A control function that causes the character positions occupied by display
controls to be displayed by repetition of the last displayable mosaic character.
5.3.2.16 Release mosaics
A control function that causes the action of hold mosaics to be stopped.
5.3.3 Mosaic graphics
5.3.3.1 The serial mosaic graphic set is given in Figure 6/T.100 and the
default conditions of the mode are shown in Table 1/T.100.
5.4 Parallel mode
5.4.1 General
5.4.1.1 The parallel mode is based on an explicit description of the display
frame. This means that the active position is moved only by action of the format
effectors or at the reception of spacing display characters. All other functions,
including display functions, are non-spacing, not depending on whether or not the
terminal needs a space on the screen to process them. It is the responsibility of
the information provider to limit the display of pages to pages to fit the
capability assumed to receive, without any modification, pages designed for lower
grade terminals.
5.4.1.2 In addition to functions described in S 3.3, the following functions
are defined.
active position addressing (APA, coded 1/15)
F: adressage de position active (APA)
S: direccionamiento de posición activa (APA)
displ
displayed on the first character position of the addressed row. If they both
range from 4/0 to 7/14, they represent respectively the row address and the
column address, in binary form with 6 useful bits, of the first characters to be
displayed.
PAGE40 Fascicle VII.5 - Rec. T.100
Fig.6/T.100/CCITT-44130 = 25 cm
Fascicle VII.5 - Rec. T.100 PAGE1
Table 1/T.100 = 25 cm
PAGE40 Fascicle VII.5 - Rec. T.100
repeat (RPT, coded 1/2)
F: répétition (RPT)
S: repetición (RPT)
This code indicates that the preceding graphics character is to be
repeated. The number of repetitions is indicated in binary form by the six least
significant bits of the subsequent character chosen from columns 4 to 7. The
character itself is not included in the count. This function does not apply to
control characters.
5.4.1.3 A supplementary set of 32 controls, of which 31 have been allocated,
are coded as a C1 set (see Figure 7/T.100). The attributes defined by such
controls become a property of the active position and move with it under the
action of format effectors or spacing display characters.
5.4.1.4 The mosaic repertoire is coded as a G1 set, of which several
representations may be defined (see Figure 8/T.100).
5.4.2 Display control functions
5.4.2.1 The display control functions are of two kinds depending on the range
of their action:
- Defined display area attributes apply to individual
character locations. Their action is limited to zones
separated by APA functions.
- Full screen attributes apply to the full screen area and
are taken as default values for defined display area
attributes.
The defined display area attributes are coded as functions from the
supplementary set of control functions (see Figure 7/T.100), with two character
escape sequences.
The full screen attribute is coded as a function from the supplementary
set of control functions with four character escape sequences (see S 5.4.2.3).
5.4.2.2 Attributes for use in the defined display area are as follows.
5.4.2.2.1 Black foreground ü
Red foreground ï
Green foreground ï
Yellow foreground ï
Blue foreground ì Causes the following characters to be written
in the colour
Magenta foreground ï indicated.
Cyan foreground ï
White foreground Φ
5.4.2.2.2 Flashing
This control function causes the characters following it to be displayed
alternatively as they would otherwise be displayed, and as spaces, under the
control of a timing device in the receiver.
5.4.2.2.3 Steady
This control function causes the action of flashing to be stopped.
5.4.2.2.4 Start box
This control function causes the characters following it to be inset or
added to a television picture, when the receiver is in the user's control. (For
further study.)
5.4.2.2.5 End box
fu
further study.)
5.4.2.2.6 Normal size
This control function causes the characters following it to occupy one
character position each.
Fascicle VII.5 - Rec. T.100 PAGE1
Fig. 7/T.100 /CCITT-44140 = 25 cm
Fig. 8/T.100 /CCITT-44150 = 25 cm
PAGE40 Fascicle VII.5 - Rec. T.100
5.4.2.2.7 Double height
This control function causes the characters following it to occupy each
its active position and the corresponding position on the previous row. (The
origin of a character is the bottom left corner of the character position.)
5.4.2.2.8 Double width
This control function causes the characters following it to occupy two
consecutive character positions on the same row, and the active position to be
moved two positions forward with every character.
5.4.2.2.9 Double size
This control function causes the characters following it to occupy the
active position, the next on the row and the two corresponding character
positions on the previous row. The active position is moved two character
positions forward with every character.
5.4.2.2.10 Black background ü
Red background ï
Green background ï
Yellow background ï Causes the following characters to be
displayed in their foreground colour
Blue background ì on a background of the colour indicated.
Magenta background ï
Cyan background ï
White background Φ
5.4.2.2.11 Transparent background
This control function causes the characters following it to be displayed
with a transparent background. This means the area not occupied by the foreground
colour takes the underlying background colour. This may be one of the eight
colours or the video picture as defined by the off screen attributes.
5.4.2.2.12 Conceal display
This control function causes the characters following it, in the same unit
although stored in the receiver, to be displayed as spaces until the user chooses
to reveal them.
5.4.2.2.13 Stop conceal
This control function causes the action of conceal display to be stopped.
5.4.2.2.14 Start lining
This control function causes the characters following in the same unit to
be lined. The shape of lining may be different depending on the character set
used. In the case of the mosaic set, the lining causes the six cells to be
separated with a background boundary.
5.4.2.2.15 Stop lining
This control function causes the action of start lining to be stopped.
5.4.2.2.16 Normal polarity
This control function causes the action of inverted polarity to be
stopped.
5.4.2.2.17 Inverted polarity
i
inverted.
5.4.2.3 FullVscreen attributes
5.4.2.3.1 FullVscreen attributes apply for the total display period and include
the border area. In addition, provisions are made for fullVrow attributes,
applying for the entire row including the border area related to that row.
FullVscreen attributes display controls are represented by four character
Escape sequences of the form ESC 2/3 2/0 Fe where Fe is taken from Figure
7/T.100.
FullVrow attributes display controls are represented by fourVcharacter
Escape sequences of the form ESC 2/3 2/1 Fe.
5.4.2.3.2 The following fullVscreen attributes need precise definition:
V Transparent background: The fullVscreen area is occupied by a picture,
which may not be part of the Videotex service (e.g. a television
picture). NonVconcealed characters appear on this picture. If they are
also displayed with defined display area transparent background, only
the foreground appears over the picture. Concealed characters are
displayed as transparent spaces.
V Conceal: The defined display area is in the fullVscreen background
colour until the user chooses to reveal it or until this attribute is
stopped by fullVscreen stop conceal.
Fascicle VII.5 - Rec. T.100 PAGE1
V FullVscreen stop conceal: This has the same action as the action of the
user on the reveal key.
5.4.2.3.3 For rowVdefined fullVscreen attributes, the following may also apply:
V lined;
V double width;
V double height.
5.4.3 Coding of the mosaic repertoire
5.4.3.1 The mosaic repertoire is designated as a G1 set invoked by the SO
function. Two alternative fonts fonts (contiguous and separated) are
proposed. The separated font is obtained by applying the lining
attribute applied to the mosaic set. The mosaic set code table is
given in Figure 8/T.100 together with examples of the fonts.
5.4.4 Default conditions
5.4.4.1 Default fullVscreen attributes
At the beginning of a display frame (initiated by function CS) the default
conditions for fullVscreen attributes are set at white foreground, black
background, single size, unboxed, revealed, steady, nonVlined.
5.4.4.2 Default defined display area attributes
After functions directly addressing a character location on the screen
(APH or APA function) the defined display area attributes are reset to the value
of the current fullVscreen attributes.
5.4.4.3 Default fullVrow attributes
The default condition of fullVrow attributes is the current value of
fullVscreen attributes.
6 Alphageometric option
6.1 General
6.1.1 Description
6.1.1.1 In the alphageometric option, the display is composed of alphanumeric
texts and pictorial drawings that are defined in terms of geometric primitives
transmitted to the terminal as drawing commands.
6.1.1.2 One coding scheme for the alphageometric option for Videotex is
described in S 6.
6.1.2 Designation and invocation of geometric codes
6.1.2.1 The designation and invocation of the alphageometric code is specified
in S 2.3.
The occurrence of the control function SO invokes the geometric primitives
in code table positions 2/0 to 7/15 inclusive. The occurrence of the code
function SI re-establishes the G0 set and the space (2/0) and delete (7/15)
functions.
PAGE40 Fascicle VII.5 - Rec. T.100
6.1.3 Geometric primitives
6.1.3.1 The coding scheme for the G1 set together with the code positions 2/0
and 7/15 for the geometric model is based on geometric primitives. Each drawing
primitive is specified in terms of Cartesian coordinates to describe the
positions, end-points, or vertices of each drawing operation.
6.1.3.2 Geometric drawings are defined in terms of the drawing primitives:
point, line, arc, rectangle, and polygon.
6.1.4 Drawing position
6.1.4.1 Drawings are positionally independent; therefore drawing primitives may
overlay each other redefining the drawing at the position.
6.1.5 Drawing space
6.1.5.1 Space for geometric drawing operations consists of a rectangular area
entirely visible on the display screen. Any area of the display screen outside of
the valid drawing area is termed a border area and it is not possible to specify
a coordinate position in a border area.
6.1.6 Picture element
6.1.6.1 The Cartesian coordinate grid is made up of square picture elements
(pixels).
6.1.7 Picture resolution
6.1.7.1 Any number of picture elements may be implemented. Hence, picture
resolution is at the discretion of terminal manufacturers.
6.1.8 Coordinate system
6.1.8.1 The coordinate specifications are defined based on a Cartesian 0 to 1
numbering scheme.
6.1.8.2 The numbering system is referenced to the visible valid drawing area
and consists of coordinates ranging from 0 to 1 on both the X and Y axes, with
coordinate values being specified as fractions of this range.
6.1.8.3 The coordinates are encoded in 2's complement notation and specified as
signed numbers to a minimum accuracy of 9 bits, including the sign bit. Increased
accuracy is obtained by additional increments of 3 bits. Unused least significant
bits are truncated when the coordinates are defined to a greater accuracy than
can be handled by the terminal.
6.1.8.4 Display screens with non-square visible areas map into the square
drawing area number system so that the origin (0,0) remains in the lower
left-hand corner. On a television-like display with a 4 : 3 aspect ratio, this
corresponds to a range of 0 to 0.999 . . . in the X axis and 0 to approximately
0.75 in the Y axis. Drawing commands addressing the entire square 0 to 1 grid are
permissible, but only the circumscribed 4 : 3 area is visible.
6.2 Drawing command
6.2.1 General
6.2.1.1 Drawing commands consist of operational codes (opcodes) and their
associated data parameters.
6.2.1.2 Opcodes describe the types of drawing operation.
etc.,
etc., depending on the degree of resolution desired.
6.2.1.4 Figure 9/T.100 is the code table for the opcodes and data
bytes or status sub-commands.
6.2.2 Opcode byte
6.2.2.1 The structure of the opcode byte is as shown in Figure 10/T.100.
6.2.3 Opcode definitions
6.2.3.1 Point
Sets the drawing beam to any position in the display space and optionally
draws a point.
6.2.3.2 Line
Draws a line based on the two given end points.
6.2.3.3 Arc
Draws a circular arc based on three points, which are the start point, a
point on the arc and the end point of the arc. A circle results when the start
and end points are coincidental and the point on the arc defines the opposite end
of the diameter. The arc may be either in outline or the area enclosed by the arc
and the chord may be filled.
6.2.3.4 Rectangle
Draws a rectangle based on specified width and height. The rectangle may
be in outline or a filled-in area.
6.2.3.5 Polygon
Fascicle VII.5 - Rec. T.100 PAGE1
Draws a closed polygon of arbitrary shape specified by the vertices. The
polygon may be in outline or a filled-in area. The maximum number of vertices is
limited to 256.
6.2.3.6 Spare
An opcode available for future definition.
6.2.3.7 Reserved
An opcode reserved for a specific future application.
6.2.3.8 Control
Provides control over the modes or attributes of the drawing commands.
6.2.4 Opcode facilities
6.2.4.1 Each opcode has four variants; these are defined by the facility bits
(b2 and b1) as shown in Figure 11/T.100. Facility field interpretations are as
given below.
PAGE40 Fascicle VII.5 - Rec. T.100
Fig. 9/T.100/CCITT-44160 = 25 cm
Fig. 10/T.100/CCITT-44170 = 6 cm
Opcode Pari Flag Descripto Facility field
ty r
field
b2 b1
b8 b7 b5 b4 0 1 0 1
b6 b3
Spare P 0 0 0 - - - -
1 0
Point P 0 0 0
1
Fascicle VII.5 - Rec. T.100 PAGE1
1 INVIS VIS ABS REL
Line P 0 0 1 JOIN SET ABS REL
1 0
Arc P 0 0 1 JOIN SET OUTLINE FILL
1 1
Rectangle P 0 1 0 JOIN SET OUTLINE FILL
1 0
Polygon P 0 1 0
1
PAGE40 Fascicle VII.5 - Rec. T.100
1 JOIN SET OUTLINE FILL
Reserved P 0 1 1 - - - -
1 0
Control P 0 1 1
1 1
INVIS Invisible ABS Absolute
VIS Visible REL Relative
FIGURE 11/T.100
Opcode facilities
6.2.4.2 b2 is binary 1
a) Point - A visible point is drawn on the display screen.
b) Line, arc, rectangle, polygon - The initial drawing position is
specified within the data bytes as absolute (X, Y) coordinates, i.e.
the initial point is set.
6.2.4.3 b2 is binary 0
a) Point - An invisible point is located on the display screen.
b) Line, arc, rectangle, polygon - The initial drawing position is the
same point as the final drawing position of the previous opcode, i.e.,
the current drawing is joined to the previous drawing.
6.2.4.4 b1 is binary 1
a) Point - The (X, Y) coordinates are relative displacements to the
preceding coordinate specifications.
b) Line - The (X, Y) coordinates for the final drawing position of a line
segment are relative displacements from initial drawing position of
that line segment.
c) Arc, rectangle, polygon - The areas established are filled or
Fascicle VII.5 - Rec. T.100 PAGE1
crosshatched.
6.2.4.5 b1 is binary 0
a) Point - The (X, Y) coordinates of the point are absolute values.
b) Line - The (X, Y) coordinates of the final drawing position of the line
segment are absolute values.
c) Arc, rectangle, polygon - The drawings are outlined.
6.3 Opcode numeric data
6.3.1 The numerical data bytes associated with an opcode immediately follow the
opcode byte and are recognized when the flag bit (b7) is binary 1. Any number of
blocks of data bytes defining pairs of coordinates or drawing displacements may
follow the drawing opcode until one of the following conditions occurs:
a) when another opcode is encountered;
b) when the shift-in code (SI) is encountered;
c) when the shift-out code (SO) is encountered;
d) when the single-shift codes (SS2 or SS3) are encountered;
e) when an escape (ESC) code is encountered.
6.3.2 The minimum number of data bytes that forms a block that defines a pair of
X, Y coordinates is three. The structure of the data block is shown in Figure
12/T.100.
Fig.12/T.100/CCITT-44180 = 6 cm
PAGE40 Fascicle VII.5 - Rec. T.100
6.4 Repeated opcode operation
6.4.1 For each of the point, line and rectangle opcodes, repeated drawing
operations will automatically be effected if the numerical data field following
the opcode byte contains more than one complete set of coordinate specifications.
A complete set of coordinate specifications is defined as all the coordinates
needed to define a point, line or rectangle drawing as a single drawing. That is,
the repeated drawing feature allows concatenated drawings to be effected without
having to repeat the opcode itself.
6.5 Geometric control opcode
6.5.1 General
6.5.1.1 The control opcodes control the drawing states of the terminal and the
interpretation of the drawing opcode attributes. The sequence of control opcodes
and their status sub-commands always precedes the opcodes for the geometric
drawing primitives of point, line, arc, rectangle, or polygon. The controls also
apply to text in shift-in (SI) mode. The four control opcodes, distinguished by
the opcode facilities bits, (b2 and b1), are given in Figure 13/T.100.
Fig.13/T.100/CCITT-44190 = 7cm
6.5.1.2 Control (value)
This control opcode defines the colour or grey scale accessed by
subsequent drawing opcodes.
6.5.1.3 Control (status)
This control opcode provides extension to a field of sub-commands.
6.5.1.4 Control (reserved)
This control opcode is reserved for future control commands.
6.5.1.5 Control (private)
This control opcode is reserved for use by terminal manufacturers to
implement proprietary non-standard functions.
6.5.2 Attributes
6.5.2.1 A number of drawing attributes may be applied to the drawing commands.
Attributes are defined by appropriate coded sequences as described below. Once an
attribute is defined, it remains valid until the attribute is redefined.
6.5.2.2 In the implementation of attributes, the level of sophistication and
complexity is left to the discretion of the implementer.
6.5.2.3 For the different drawing attributes and their feature levels see
Recommendation F.300.
6.5.3 Control (value)
(
(only the 6Vbit data portion of the 8Vbit byte is shown).
Fig.14/T.100/CCITT-44200 = 8 cm
6.5.4 Control (status) and status subVcommands
6.5.4.1 The control (status) opcode accesses a field of status subVcommands
(columns 4, 5, 6 and 7) which define in detail all the modes of drawing operation
or attributes. The sequence is always control (status) followed by a status
subVcommand, which in turn may or may not be further followed by parameter data
bytes. Figure 15/T.100 gives the codings of the status subVcommands. Detailed
definitions of the status subVcommands are given below.
6.5.4.2 (4/0) ClearVtoVblack
This subVcommand clears the entire display to black.
6.5.4.3 (4/1) ClearVtoVtransparent
This subVcommand clears the entire display of the screen to transparent.
By transparent is meant that conventional television pictures can be mixed with
Videotex images or text.
6.5.4.4 (4/2) ClearVtoVblack and initialize
This subVcommand clears the entire display to black and resets the
terminal to the default mode.
6.5.4.5 (4/3) ClearVtoVcurrent colour
This subVcommand clears the entire display to the colour currently
specified by the control (value) opcode sequence.
6.5.4.6 (4/4) Domain (3 bytes)
The block of numerical data that follows an opcode contains 3 bytes. This
is also the default condition.
6.5.4.7 (4/5) Domain (4 bytes)
The block of numerical data that follows an opcode contains 4 bytes.
Fascicle VII.5 - Rec. T.100 PAGE1
6.5.4.8 (4/6) Domain (5 bytes)
The block of numerical data that follows an opcode contains 5 bytes.
PAGE40 Fascicle VII.5 - Rec. T.100
6.5.4.9 (4/7) Domain (6 bytes)
The block of numerical data that follows an opcode contains 6 bytes.
6.5.4.10 (4/8) Drawing (blink-off)
Terminates the drawing (blink-on) status sub-command.
6.5.4.11 (4/9) Reserved
6.5.4.12 (4/10) Drawing (blink-on) (or flashing)
This sub-command causes the drawing (or text) that follows to flash in a
repetitive manner for the purpose of drawing attention. In general, an object of
any colour or grey scale may be blinked, but in some implementations, blinking
may be restricted.
6.5.4.13 (4/11) Reserved
6.5.4.14 (4/12) Tonal (colour)
This sub-command designates that the Control (value) sequence carries
colour information (see S 6.5.3).
6.5.4.15 (4/13) Tonal (grey scale)
This sub-command designates that the Control (value) sequence carries grey
scale information (see S 6.5.3).
6.5.4.16 (4/14) Reserved
6.5.4.17 (4/15) Reserved
6.5.4.18 (5/0) Line (solid) (See Note)
This sub-command indicates that the drawing lines will be solid. This is
also the default condition.
6.5.4.19 (5/1) Line (dotted) (See Note)
This sub-command indicates that the drawing lines will be dotted in
texture.
Fascicle VII.5 - Rec. T.100 PAGE1
Fig.15/T.100/CCITT-44210 = 25 cm
PAGE40 Fascicle VII.5 - Rec. T.100
6.5.4.20 (5/2) Line (dashed) (See Note)
This sub-command indicates that the drawing lines will be dashed in
texture.
6.5.4.21 (5/3) Line (dot-dashed) (See Note)
This sub-command indicates that the drawing lines will be dot-dashed in
texture.
Note - The line texture pattern is referenced to the absolute coordinate
grid of the display screen so that the texture pattern aligns between drawing
commands.
6.5.4.22 (5/4) Fill
This sub-command fills the enclosed area drawn in the colour specified by
the current Control (value) sequence.
6.5.4.23 (5/5) Reserved
6.5.4.24 (5/6) Fill (border highlight black)
This sub-command fills enclosed area drawn as S 6.5.4.22 above and the
circumscribing border is highlighted in black.
6.5.4.25 (5/7) Reserved
6.5.4.26 (5/8) Reserved
6.5.4.27 (5/9) Reserved
6.5.4.28 (5/10) Reserved
6.5.4.29 (5/11) Reserved
6.5.4.30 (5/12) Wait (timed)
This sub-command causes a delay of a specific time in processing and
display. The length of wait is specified in tenths of a second, either by one
associated parameter byte (6 bits for up to 6.3 s) or two parameter bites (12
bits for up to 6.8 m).
6.5.4.31 (5/13) Wait (indefinite)
This sub-command causes an indefinite wait. This may be achieved by the
terminal responding with a pause flow control character (DC3 in C0 set) towards
the computer. The wait is then terminated when the terminal sends a resume data
flow character (DC1 in C0 set).
6.5.4.32 (5/14) Reserved
6.5.4.33 (5/15) Reserved
6.5.4.34 (6/0) Text format
This sub-command has an associated data byte, which defines the text
formats as follows:
Bit b6 = 0: Free format, i.e. character strings are wrapped around on the
right margin.
Bit b6 = 1: Annotation format, i.e. character strings are in fixed
positions on the screen.
Bit b5 = 0: In free format, character strings are broken on a character
boundary.
Bit b5 = 1: In free format, character strings are broken on a word
boundary.
b4, b3: Defines character rotation as shown in Figure 16/T.100. Rotated
strings of characters proceed in the direction of rotation.
However, all other format controls on characters such as APB,
APF, APD, APU and APR have their (unrotated) orientation
meanings.
b2, b1 = 0.0: Vertical spacing = 1.0
b2, b1 = 0.1: Vertical spacing = 1.5
b2, b1 = 1.0: Vertical spacing = 2.0
b2, b1 = 1.1: Vertical spacing = 2.5
Fig.16/T.100/CCITT-44220 = 4 cm
6.6 Default conditions
6.6.1 The default conditions of the attributes for the alphageometric coding
scheme are summarized below:
Reference
1) Control (value): White S 6.5.3
2) Tonal control: Tonal (colour) S
6.5.4.14
3) Domain: 3 bytes (9 bits) S
6.5.4.6
4) Drawing: Blink-off S
Fascicle VII.5 - Rec. T.100 PAGE1
6.5.4.10
5) Line control: Solid line S 6.5.4.18
6) Fill: Solid fill
(no highlight) S
6.5.4.22
7) Text format: a) Free format S
6.5.4.34
b) Break on character boundary ü with
bits 1
c) No rotation ì to 6 set to "0"
d) Vertical spacing = 1.0 Φ
7 Alpha-dynamically redefinable character sets (DRCS) option
7.1 General
7.1.1 A DRCS is a set of characters whose shapes are sent from the data-base and
down-loaded via the line. It may be used to represent alphabetic characters,
special symbols, or picture element symbols for constructing fine graphics. Once
loaded, the DRCS are regarded as members of a library that can be designated by
appropriate ESC sequences as G0, G1, G2, G3 sets. Several schemes for the DRCS
option are possible. One scheme is described in S 7 in the context of a general
architecture. When used in its alphanumeric mode DRCS may be employed as a part
of the alphabetic representations of any other Videotex option and in that case,
the attributes associated with that option are to be used.
7.2 General architecture for down-loading DRCS
7.2.1 Initiation
The down-loading process is initiated by a designation and invocation
sequence. This sequence is followed by one or more of the following functions.
7.2.2 Identification of character set (ICS)
identifie
identifies the escape sequence used for the designation of the character set.
7.2.3 Select coding method (SCM)
This function defines the type of coding used to describe the DRCS
character.
7.2.4 Select dot composition (SDC)
This function defines the number of bits horizontally and vertically in a
character matrix, the number of bits per pixel, the number of grey scale levels
and the number of colours accessible within a character position.
7.2.5 Pattern transfer (PT)
This is the active part of the downVloading process. It defines the code
location of the first character and provides instructions and data to draw
characters. It may also incorporate an error checking procedure.
7.2.6 DownVloading termination procedure (DLT)
The downVloading process is terminated by a specific procedure, which may
include acknowledgement.
7.3 A possible coding scheme for the DRCS option
7.3.1 Initiating sequence
The initiating sequence is ESC Fs followed by x bytes indicating the
length of the loading data block, where x is for further study.
7.3.2 Termination procedure
The downVloading process is terminated by means of counting the length of
the loading data block. See ' 7.3.1.
7.3.3 Designation and invocation of loaded DRCS
7.3.3.1 Once loaded into the terminal, the DRCS is placed into a library. This
library is used in the context of ISO 2022 in the 7Vbit environment as
implemented in earlier sections. Before invoking the designated DRCS, it is
required to designate a C1 set to be associated with it. For the scheme described
herein any of the C1 sets (to be registered) that are defined in '' 2.2 and 2.3
may be used.
7.3.3.2 The designation sequence will be of the form ESC I1, 2/0, (I3 . . . In)
F. I1 will be 2/8, 2/9, . . . or 2/15. I3 . . . In are optional, and if present
together with F, will identify the set. Means for associating the designating
sequence with the process of defining the character shapes will be for further
study.
8 Alphaphotographic option
8.1 The alphaphotographic option is used to render an image by the
transmission and display of individual picture elements.
PAGE40 Fascicle VII.5 - Rec. T.100
8.2 This option may include both continuousVtone images such as pictures of
faces, etc., as well as patternVoriented techniques for the display of pictures,
including graphics, Latin and nonVLatin characters for text, etc. The system
features and attributes include colour and monochrome.
8.3 The detailed system proposals are for further study.
9 Service enhancements
9.1 Introduction
9.1.1 Many Administrations are offering or considering the introduction of a
Videotex service, and it is recognized that this Recommendation may influence
some of their decisions. While the other sections of this Recommendation contain
details of those aspects of an international Videotex service that could be
agreed upon, this S 9 identifies certain potential enhancements (features or
attributes) that some Administrations believe need to be considered in future
developments.
9.1.2 It is recognized that some of these potential enhancements may only exist
on national Videotex services, while others may have international application.
However, an enhancement that begins on a national service only could become
international in the future. Therefore, it is considered desirable to have
international coordination of future enhancements.
9.2 General
9.2.1 The growth of international Videotex services during the years following
the publication of this Recommendation will be greatly affected by the specific
specifications contained in the other parts of this Recommendation. However, some
Administrations believe that experiments with and/or implementation of certain
enhancements will allow the development of an international service that provides
a range of capabilities that will maximize the desirability and utilization of
Videotex service.
9.2.2 Some of the potential enhancements to Videotex service, national or
international, are presented in the following. This is for the purpose of
identifying to interested Administrations those enhancements that warrant serious
consideration in the view of the CCITT, but which presently lack enough details
to obtain the full agreement of all Administrations.
9.2.3 The enhancements have been grouped into three categories in order to
assist the reader in understanding the application of each individual enhancement
(which may be referred to by some Administrations as attributes or features or
some other descriptive phrase) and to prompt an orderly investigation of them:
a) display-related enhancements;
b) transmission-oriented enhancements;
c) system level enhancements.
9.3 Display related enhancements
9.3.1 Most of the currently planned and/or offered services utilize images
created with only eight colours, which are formed by the various combinations (on
or off) of three primary colours - red, green and blue. Limiting Videotex to
eight colours is an unnecessary restriction, since the electronic emission
devices controlling the red, green and blue colours can be caused to have more
than just the two states of on or off. For example, with just eight different
states or levels, a potential of 512 colours exist. Additionally, for those
services that use a matrix-oriented screen (e.g. a mosaic graphic mode),
different colours could be identified for foreground symbols to those for
background areas.
9.3.2 The ability to simulate motion (i.e. animation) is a potential enhancement
that can be achieved by several means. These include:
a) alternating between slightly different display frames stored in the
terminal;
b) dynamically altering the colour of portions of the display image,
making them appear or disappear by redefining the colour table (an
image disappears when its colour is set to the same colour as the
surrounding area);
c) execution of a resident program to redefine the image at a controlled
rate.
9.3.3 The flashing of symbols or areas of the display has typically been limited
to changing the foreground symbol (in the case of a matrix-oriented screen) to
the background colour, momentarily, or some other single-state change. An
enhanced flashing capability could allow for different rates of change and for
various conditions associated with each change (e.g. colour X to colour Y, rather
Fascicle VII.5 - Rec. T.100 PAGE1
than foreground colour to background colour or foreground colour to black).
9.3.4 Different pictorial (text and graphic) symbols may be developed that
extend the repertoire of a Videotex service. This may be a fixed extension
defined in the terminal memory, or can be a modification to the existing memory
by downloading from the data base. The range of extended symbols includes
different fonts of existing symbols, smoothed mosaic graphics, or other unique
symbols.
9.4 Transmission oriented enhancements
9.4.1 The exchange of information directly between terminals, without
communicating with a Videotex service may be permitted by some Administrations as
an enhanced capability, and could be of value to the users of Videotex terminals.
Such a capability would require the existence of control functions that might
not, otherwise, be available in some terminals that utilize certain existing or
planned national Videotex services, but this should not cause any
incompatibilities with such services.
9.4.2 The optimization of the coded character stream for maximum data rate is a
valuable enhancement. This might be accomplished by utilizing an 8-bit per word
coding format rather than the 7-bit per word format currently planned by most
Administrations, coupled with a related decision on the line or link level
protocol selected. The selection of an 8-bit per word format could permit a more
efficient transmission of data.
In addition, such techniques as run-length-encoding might be specified in
the Recommendation to reduce the transmission of unnecessary or redundant data.
The choice of higher speed modems/circuits is also considered by some
Administrations as a way to optimize the transfer of data within or between
Videotex services.
9.4.3 For some applications of a Videotex service, sophisticated error detection
and correction schemes may be required and should be considered with other
transmission-oriented enhancements on future Videotex services.
9.5 System level enhancements
9.5.1 An enhancement seriously considered by some Administrations is the
provision of a Videotex service that provides visual information, augmented by
audio information. This capability could permit access by a terminal to
visual-only information in a data base, and to visual/audio information in the
same or other data base. The audio information might be associated with the
visual information, or treated separately, or even alternately, depending upon
the implementation. The audio information might be analogue or digitally encoded
or handled as a composite signal.
9.5.2 The provisioning of peripheral input/output devices associated with the
Videotex terminal is an important enhancement for future services. These could
include magnetic storage devices for recording visual/audio information as
received by the terminal, or recorded locally by the terminal for subsequent
transmission to a data base or other terminal. Various hard copy printing devices
could also be provided, with their design based upon the specific visual
capabilities of the terminal, e.g. degree of resolution and colour of the image
on the display screen.
10 Line and end-to-end protocols
10.1 The purpose of S 10 is to describe the protocols needed for international
Videotex transactions. Section 10 contains an introduction only. Detailed
consideration is left for further study.
10.2 The transfer of information from a data base of one service to a user of
another service may be split up into two parts:
a) the information transfer from one service to another;
b) the information transfer from the service to the user.
10.3 Line protocols
10.3.1 Line protocols between services
10.3.1.1 The international line between national data base computers must be
able to transmit transparent coding schemes identified in this Recommendation and
accept the protocols of S 10.4.
10.3.2 Line protocols between service and user
10.3.2.1 The following protocol functions should be studied:
PF1: Start of coded data starts a sequence of data to be understood as
textual information (could be coded as STX).
PF2: Start of prefix causes the following bytes to be understood as a
prefix containing framing information including codes for error check
PAGE40 Fascicle VII.5 - Rec. T.100
and/or correction (could be coded as SOH).
PF3: End of coded data ends a sequence of data to be understood as
textual information (could be coded as ETX).
PF4: End of frame. Ends a frame of data and requests for reverse
transmission and give an answer (could be coded as ETB).
PF5: Answer given in case of error free reception or when error
correction is possible (could be coded as ACK).
PF6: Answer given in case of errors when no error correction is possible
(could be coded as NAK).
10.3.2.2 It is noted that TC1 to TC10 (SOH to ETB of Recommendation T.50) are
intended to control the transmission of information over transmission networks.
The use of these functions may therefore not be used as part of the information
stream from one service to another.
10.3.2.3 The use of protocol functions is for further study.
Fascicle VII.5 - Rec. T.100 PAGE1
10.4 Protocols for communicati n between services on the
application level
10.4.1 General
10.4.1.1 International exchange of information between national Videotex
services may be sent in blocks, here called messages. For efficient use of
networks and communication equipment it is important to design the messages to
minimize the capacity needed for applications that are frequently used in
Videotex services.
10.4.2 Types of message elements
10.4.2.1 A complete message is composed of message elements. Each element
contains an element identifier, a data field and an indication of element length
(explicit or implicit).
10.4.2.2 Transmit a standardized function
Codes for functions may be different from the character sequences, sent by
the user.
10.4.2.3 Transmit a service message
A service message is a frame that is transmitted to the subscriber,
without erasing the screen, moving the active position of the cursor, or changing
the contents of the previous display.
10.4.2.4 Transmit a service message code
The proper service message is generated by the receiving system and
transmitted to the subscriber.
10.4.2.5 Transmit a frame
Billing and other additional information is to be transmitted together
with the frame.
10.4.2.6 Transmit data block
By data is meant all types of data that are not listed under separate
items, e.g. software. It is necessary to transmit block length when transmitting
transparent data.
10.4.2.7 Transmit field description
A field description is a list of positions on the screen, where an
application program expects additional information to be filled in, either by the
user or by the application program itself. It includes also format and type of
information which allows simple syntax control in the host computer.
Three formats are recognized; strings, which means any combination of
graphical characters including space, integers (0-9), and free format.
A field may be of input and/or output type. An input field is a field
where the information is user originated. An output field is a field in which the
information is filled in by the application program.
10.4.2.8 Transmit a user message to an application
A user message is the data that is filled in by the user according to a
field description. It is sent to the external computer. The transmission is
initiated either by a send-function if it is available, or when all input fields
are filled. The use of a delimiter causes the rest of the field to be filled with
spaces. If a delimiter is used in the first position of a combined input and
output field, the contents remain unchanged.
10.4.2.9 Transmit an application message
An application message is a block of data to be filled into the output
fields, defined by a field description. It may be sent either in the same message
as the field description, or after.
10.4.2.10 Request information on terminal capability
(For further study.)
10.4.2.11 Transmit information on terminal capability
(For further study.)
PAGE40 Fascicle VII.5 - Rec. T.100
10.4.2.12 Error condition element
The detection of contradicting information in a system will result in an
error condition message to the other system, e.g. data with a format different to
the corresponding field description. The entire message causing the error will be
ignored, and it is the responsibility of its transmitting system to handle the
error properly.
10.5 User to data base protocol
10.5.1 In order to use Videotex service, a user must be able to generate a set of
functions which enables him to access and use different applications. A set of
user functions is listed in Recommendation F.300.
10.5.2 The minimum set of characters to code these functions contains the digits
0-9 and two other symbols. For some applications however, the generation of
alphanumeric as well as pictorial and attribute information and other control
characters may be needed.
10.5.3 Although it is desirable that all Videotex services employ the same keying
sequences and visual identifiers for these functions, there are historical
reasons why there will be different manners of coding the same user functions.
10.5.4 Accessing the national service of another country using an international
connection between services is possible, if the user obeys the function coding
rules of the service of the other country. It is, however, possible that the
local data bank may be able to translate the local keying sequence into the
appropriate command in a national service level (see S 10.4.2.4). This subject is
left for further study.
11 Interworking with other services
11.1 Telex-Videotex
11.1.1 Telex is a message transfer service and therefore, interworking between
telex and Videotex should be limited to the exchange of alphanumeric text between
terminal equipments.
11.1.2 Only the graphic characters of the Videotex graphic character repertoire
corresponding to International Telegraph Alphabet No. 2 should be used to compose
messages.
11.1.3 The message format will be limited by the Videotex page format.
11.1.4 Telex can only display alphanumeric information without the capability of
displaying the other attributes of Videotex.
11.2 Teletex-Videotex
11.2.1 Graphic character repertoire
11.2.1.1 The Teletex and Videotex graphic repertoires are largely identical. The
following fallback representations of Videotex characters (see Table 2/T.100),
may be transcoded at a Videotex-Teletex interworking facility.
TABLE 2/T.100
Identifier Videotex character Fallback
representation
SM30 <- < SA03
SM31 -> > SA05
SM32 í SP03
SM33 ! SP02
SP19 æ ` SP05
SP20 '
Fascicle VII.5 - Rec. T.100 PAGE1
` SP05
SP21 " " SP04
SP22 " " SP04
SM12 -- - SP10
MG01 to MG63 Block graphics / SP12
11.2.1.2 For Teletex terminals having the ability to present the Videotex
character repertoire in its entirety, the need for this transcoding disappears.
Therefore, on initial call establishment, a determination of the terminal
display/printing capabilities must be made by handshaking.
11.2.2 Control functions
11.2.2.1 Transcoding of the Videotex attribute control functions is for further
study.
11.2.3 Format
11.2.3.1 Interworking between Videotex and Teletex will be limited to the
Videotex display frame format.
11.3 Videotex-facsimile
(For further study.)
11.4 Videotex-Teletex
(For further study.)
PAGE40 Fascicle VII.5 - Rec. T.100
ANNEX A
(to Recommendation T.100)
Part of the code extension scheme of ISO 2022
Fig. Annex A CCITT-35951 = 23 cm
Fascicle VII.5 - Rec. T.100 PAGE1
ANNEX B
(to Recommendation T.100)
Repertoire of graphic characters
B.1 General
B.1.1 This annex defines the basic graphic repertoire of the international
Video service. This repertoire consists
of the total range of non-pictorial symbols, which may be
communicated between Videotex services and terminals by means of
coded character sets for Latin-alphabet based languages.
B.1.2 The repertoire of graphic characters defined in this part of
the Recommendation consists of:
a) Latin alphabetic characters, listed in S B.2, which comprise:
- the 52 small and capital letters of the basic Latin alphabet,
- combinations of basic Latin letters and diacritical marks,
- special alphabetic characters, which are neither basic Latin
letters nor combinations of basic Latin letters and diacritical
marks,
b) non-alphabetic characters, listed in S B.3, which comprise decimal
digits, currency signs, punctuation marks, arithmetic signs and
miscellaneous symbols that have individual special meanings.
B.1.3 A diacritical mark has no meaning as an individual character but is used
only in combination with a basic Latin letter to form an accented letter or an
umlaut.
B.1.4 The repertoire of graphic characters defined in this part of the
Recommendation contains a limited set of accented letters and umlauts.
B.2 Latin alphabetic characters
B.2.1 The repertoire of Latin alphabetic characters is identical to that
specified in S 3.2.2 of Recommendation T.61 (for the Teletex basic repertoire of
graphic characters).
B.3 Non-alphabetic characters
B.3.1 Decimal digits (0 to 9), currency signs, arithmetic signs, subscripts and
superscripts and fractions are as specified in SS 3.2.3.1, 3.2.3.2, 3.2.3.4,
3.2.3.5 and 3.2.3.6 of Recommendation T.61.
B.3.2 Punctuation marks are as specified in S 3.2.3.3 of Recommendation T.61,
with the exclusion of SP09 (low line) and the addition of SP19 to SP22, which are
as shown in Table B-1/T.100.
B.3.3 Miscellaneous symbols are as shown in Table B-2/T.100.
B.3.4 The lists in Tables B-1/T.100 and B-2/T.100 are composed as described in
the following.
The first column contains the identifier of each character, assigned in
accordance with the identification system explained in Annex C of Recommendation
T.61.
The second column presents the graphical representation of the character.
The third column specifies the name or the description of the character.
TABLE B-1/T.100
Punctuation marks
Identifier Graphic Name or description
SP19 æ Single quotation
mark left
SP20 ' Single quotation
mark right
SP21 " Double quotation
mark left
SP22 " Double quotation
mark right
Note - In Videotex (and Teletex), quotation mark, apostrophe and
comma are independent characters that cannot have the meaning of
diacritical marks.
TABLE B-2/T.100
Miscellaneous symbols
Identifier Graphic Name or description
SM01 ## Number sign
SM02
PAGE40 Fascicle VII.5 - Rec. T.100
% Percent sign
SM03 & Ampersand
SM04 * Asterisk
SM05 @ Commercial at
SM12 - Horizontal bar
SM13 | Vertical line
SM17 m Micro sign
SM18 W Ohm sign
SM19 o Degree sign
SM20 o Ordinal indicator, masculine
SM21 a Ordinal indicator, feminine
SM24
Fascicle VII.5 - Rec. T.100 PAGE1
S Section sign
SM25 Paragraph sign, pilcrow
SM26 . Middle dot
SM30 <- Leftward arrow
SM31 -> Rightward arrow
SM32 Upward arrow
SM33 Downward arrow
PAGE40 Fascicle VII.5 - Rec. T.100
