ftp.whtech.com/ftp.whtech.com.tar/ftp.whtech.com/articles/limanews/ASCII.TXT

Text File | 2006-10-19 | 6KB | 170 lines

ORIGINALLY PUBLISHED IN LIMA NEWSLETTER NOVEMBER 1990

          All About Character Sets
          By:  Andy Frueh, Lima UG

     I had written about using CTRL and FCTN keys as a form of "macro" since
practicaly every CTRL keypress represents a keyword.  All of this got me
thinking about the TI's character set, and a lot of the information pertaining
to it.  What follows is a lot of miscellaneous data on the ASCII characters.

     Most people don't take much interest in character sets.  You hit a key, a
symbol shows up on the screen.  A code is assigned to every character.  These
codes are numerical values from 0 to 255.  A space (or more appropriately
called a blank) is code 32, a capital D is 68, etc.  The computer knows at
least two things about each character.  Its graphic (what it looks like) and
its assignment (what keys you press to get that character).  You can use both.
For example, when you type in a program and use PRINT, DISPLAY, DISPLAY AT, or
INPUT/LINPUT with a prompt, you are using the graphic representation.  When you
use an HCHAR or VCHAR, you must use the actual numerical ASCII code.  You also
do this with the CALLS KEY subprogram.  The function ASC and CHR$ also use
numerical representations.

     This information is all in the manual.  There is some data that is not in
the manuals, or is covered in technical jargon.

     When you use VCHAR, HCHAR, and CHR$, you can actually use values up to
32767.  256 is continually subtracted until you get a value in the 0-255 range.
Not all codes have graphic representations.  These are usually "empty" and
appear as the blank/space character.

0 - Undefined (no key assignment/graphic)

1 to 15 - Function keys (see chart 1).  Most of these can be accessed in
programs using CALL KEY, but not as response to ACCEPT AT/INPUT statements.
They have no graphic (unless a program gives it one.  In that case, typing the
character gives the pattern it was assigned.)

16 to 29 - Undefined (these are the same as 0 since they don't have graphics or
key assignments and there really isn't an easy way to give them either.)

30 - This is the cursor, usually a black square.  An assembly routine is
usually needed to redefine its graphic.

31 - This is the screen border.  It is a blank and the color of the border
around the screen, not the color of the screen itself.  It has no key
assignment.

32 to 126 - The "standard" characters (see chart 2).  These are such things as
letters, numbers, and symbols used in everyday typing.  They can be redefined
in a program.

127 to 159 - These are called "user-defined" characters (see chart 3).  They
originally have no graphic.  The manual is incorrect in that it says when a
program ends, the characters blank out.  This is not true.  Also, these keys
have key assignments and are used to represent BASIC keywords at first.  All
but one requies you press CTRL and another key.  Character 127 used the FCTN
key.

160 to 175 - Undefined (see above)

176 to 198 - These characters have key assignments (see chart 4), but no
graphic, and no easy way to give any.  They can be used with CALL KEY, but can
not be displayed.

199 to 255 - Undefined (see above)

     Even those which I labeled as undefined have a use.  You can access them
through CHR$ and ASC functions.  They are useful as markers when manipulating
strings.  If you are transmitting data from the TI to another computer, the
other computer may have representations for these characters.

     Finally, each character string has a code between 0 and 255, accessable
through CHR$ and ASC.  The SEG$ function will let you address individual
characters in strings, and the apersand operator (SHIFT 7) called concatenation
will allow you to compose a string out of individual characters.  If you have a
program that keeps track of thousands of small integers and you can't fit them
in available memory, strings are probably the answer.

Chart 1 - Function Key Codes
CODE   KEY
1      FCTN 7 (AID)
2      Not useable in BASIC.  It is associated with FCTN 4, but you can't
       really use this in BASIC.  In Extended BASIC, an ON BREAK will work.
3      FCTN 1 (DELETE)
4      FCTN 2 (INSERT)
5      Used with QUIT.  In Extended BASIC, a CALL LOAD disables this key.  I am
       not sure whether you can use FCTN = and a key code of 5 in a program.
6      FCTN 8 (REDO)
7      FCTN 3 (ERASE)
8      FCTN S (left)
9      FCTN D (right)
10     FCTN X (down)
11     FCTN E (up)
12     FCTN 6 (PROCEED)
13     ENTER
14     FCTN 5 (BEGIN)
15     FCTN 9 (BACK)

Chart 2 - Standard ASCII Characters
     These are in the User's Guide, Extended BASIC manual, and both BASIC's
Quick Reference Card.  Refer to these.  Note that character 127 shouldn't
really be in this group.  Characters in this group include 32 to 126.


Chart 3 - User Defined Characters
CODE   KEY
127    FCTN V
128    CTRL ,
129    CTRL A
130    CTRL B
131    CTRL C
132    CTRL D
133    CTRL E
134    CTRL F
135    CTRL G
136    CTRL H
137    CTRL I
138    CTRL J
139    CTRL K
140    CTRL L
141    CTRL M
142    CTRL N
143    CTRL O
144    CTRL P
145    CTRL Q
146    CTRL R
147    CTRL S
148    CTRL T
149    CTRL U
150    CTRL V
151    CTRL W
152    CTRL X
153    CTRL Y
154    CTRL Z
155    CTRL .
156    CTRL ;
157    CTRL =
158    CTRL 8
159    CTRL 9

Chart 4 - Key Assigned/No Graphic
These characters aren't discussed
much in TI documentation.
CODE   KEY
176    CTRL 0
177    CTRL 1
178    CTRL 2
179    CTRL 3
180    CTRL 4
181    CTRL 5
182    CTRL 6
183    CTRL 7
184    FCTN ,
185    FCTN .
186    FCTN /
187    CTRL /
188    FCTN 0
189    FCTN ;
190    FCTN B
191    FCTN H
192    FCTN J
193    FCTN K
194    FCTN L
195    FCTN M
196    FCTN N
197    FCTN Q
198    FCTN Y
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