8bitfiles.net/archives/archives.tar/archives/genie-commodore-file-library/Information/TTD_ASCII-BAUDOT.TXT

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---The History of the HEX---

   The Handicapped Educational Exchange was developed under a grant from  the
Dept. of Education to serve the handicapped community.  The first  grant, in
1979, served to fund the development of a smaller system which  was first
placed into operation in the early part of 1980.  It employed a  6800-based
microcomputer, handled only one caller at a time, and served  through the start
of 1983.  It was developed by Robert Bruninga of AMRAD, the Amateur Radio Re-
search & Development Corporation, which was the  grantee for this project.

   The hardware for the second system (HEX2) was bought under the second  year
of the grant. The system was designed and built by Richard Barth, an  AMRAD
member and a consultant in microcomputer applications to deaf  communications.

It employed a 6809, had a larger data storage capacity  and greater speed, and
could handle several users at the same time.  It  was connected to two phone
lines. It began running part time for tests in  March of 1983, and started
operational service in April of that year.

   The current system operates on an XT clone with 640K of RAM and a 30  meg
hard disk. The software was written in the C programming language by  Richard
Barth. It accepts calls from Telecommunications Devices for the  Deaf
(TDD/TTYs) and at 300 baud ASCII using a Model CM-4 modem by Phone- TTY Inc. of
Hackensack NJ.  A separate line will operate at 300 and 1200  baud once softwa-
re debugging is complete, using an Everex modem.

   Design, construction and operation of the HEX are unfunded, the costs being
shared by AMRAD and the system operator.  AMRAD, the Amateur Radio  R&D Corp.,
is described in a separate INFO file.


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>>>>>>>>>>>>>>>>>>>>>>>  TTDs or TTYs :

               TELECOMMUNICATIONS DEVICES FOR THE DEAF

     There are over 3000 Telecommunication Devices for the Deaf in use in the
greater Washington D.C. area and estimates range as high as 25,000 nationally.

The deaf have been using these devices for over fifteen years, to  communicate
among themselves and more recently, with a growing number of  organizations
with TTY numbers to allow phone access to deaf users. See the  INFO files for
some numbers. Although originally the majority of devices were  surplus
"teletype" machines donated by the phone company and the military,  these
mechanical printers are rapidly being replaced by more modern devices  offering
special features as well as reductions in size and weight.  A  portable device
about the size of a calculator is available for under $200.

   The following shows the differences between the modems used.  The owner of
a computer can rather easily modify his software to convert between the ASCII
code used in microcomputers and the code used by the deaf TTY.  Often, it is
harder to get a modem which is compatible both with a computer and with the
TTY. The usual procedure is to convert an ASCII (Bell-103 compatible) modem
 or build a TTY modem from scratch.

     There are several differences between protocols used by ASCII terminals
and by the TTY. The following attempts to clarify these.


                        ASCII DATA        DEAF TDD
          FEATURE    COMMUNICATIONS    COMMUNICATIONS
          -------  ------------------  --------------

           CODE          ASCII             Baudot

           SPEED      110/300 baud       45.45 baud

           MODE     full/half-duplex   2 way simplex

           MODEM   Bell 103 ORIG/ANS     Weitbrecht

           MARK      ORIG 1270 Hz         1400 Hz
                     ANS  2225 Hz

           SPACE     ORIG 1070 Hz         1800 Hz

                     ANS  2025 Hz


 In the Weitbrecht modem, tones are only transmitted for the duration of the
character so the line is available for transmission in either direction. In
practice the mark tone is retained for as much as a half second before being
squelched.

 Notice also that the mark is high for the Bell 103 and is the low tone for
the Weitbrecht. This means that in converting a a Bell 103 modem to TTY use,
the data will be inverted from RS-232 and the mark hold circuitry will need
to be inverted.

 Line supervision is also different in these modems. In -103 protocol, the
presence of the tone carriers gives positive indication of the status of each
end of the link. In the Weitbrecht case, however, the absence of tones except
while characters are being transmitted results in there being no positive way
to test the status of the other end of the communications link. To aid the
deaf, a lamp is provided on most Weitbrecht modems which varies in intensity
proportional to signals on the line so that the ringing and busy signals are
recognizable.


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>>>>>>>>>>>>>>>>>> THE SPONSOR OF HEX BBS :

---AMRAD---

   The Amateur Radio Research and Development Corporation (AMRAD) is a group
of radio amateurs and computer experimenters based in the Washington D.C.
area. Many of its members are professionals in the engineering, communications
, and computer fields.

   The group meets the first Monday of each month in the Patrick Henry Library
in Vienna, Virginia. Meetings begin at 7:30 and continue through 9:00 PM. A
speaker on some technical subject of interest is heard at each meeting;
interpreters are provided upon request for deaf persons attending.

   AMRAD operates a bulletin board on [phone] which runs 24 hours a day
and deals with general hobby-oriented subjects. The operator is Terry Fox,
WB4JFI. The HEX, also run by AMRAD, is operated by Richard Barth, W3HWN. AMRAD
operates a radio repeater on 147.81/21 MHz, which is available to any licensed
radio amateur. The chief maintainer of the repeater is Jeff Brennan, WB4WLW. It
carries both voice and digital traffic. Another AMRAD repeater is operated by
Sandy Sanders, WB5MMB on 147.585 MHz and operates simplex, carrying packetized
data only.

   AMRAD is involved in a number of technical experiments, which currently
include packet switching of computer data and spread spectrum communications in
the amateur bands. Plans are underway, in cooperation with AMSAT, to develop
international packet switching networks via amateur satellite.

   Dues for AMRAD are $15.00 a year, and include a monthly newsletter which
provides a summary of work in progress and serves to tie together members
throughout the world.


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>>>>>>>>>>>>>>>>>>>>>  USING COMPUTERS AS TDDS:

 ---COMPUTER TDDs---

   It is possible to use a home computer as a TDD. This requires programming to
convert the ASCII code used by the computer to the Baudot code used by the TDD,
and vice versa. It is usually necessary to add a special modem, unique to the
TDD, that is named after its developer, Robert Weitbrecht. A description of
this modem, and the characteristics of the TDD, are in INFO file T.

   John W. Spalding of Atlanta, Georgia has developed programs for the  Radio
Shack Color Computer which permit it to serve as a TDD without the  need for a
special modem. This design is a major breakthrough since  unavailability of
these modems has been a problem for those trying to make  a computer talk to a
TDD. Mr.  Spalding has placed his creations in the  public domain, making them
available without charge to anyone who wants  them. He has sent HEX the source
code; you may read it by downloading  TDD54.ZIP and TDD56.ZIP from file area
two.

     All CoCo software is in assembly language for the 6809. They are source
only; machine code is not included. If you want a paper copy including machine
language, send a stamped self addressed business envelope to:

  Handicapped Educational Exchange
  11523 Charlton Drive
  Silver Spring MD 20902

Machine code for TDD3.5 is available from HEX on cassette tape and for TDD4.3
in a 2716 EPROM. The EPROM must be mounted in a ROM pack to be inserted in the
side of the CoCo. An empty ROM pack is available for $9.95 from Spectrum
Projects, P.O. BOX 21272, Woodhaven NY 11421 or call [phone]. Other
sources for these ROM packs may also be available. When you have received your
ROM pack,  contact HEX for information on getting an EPROM.

   Mr. Spalding has also written TDD software for the IBM-PC that, like his
CoCo software, does not require a modem. This is also in the public domain and
will be provided gratis to anyone who sends HEX a blank, 5 1/2 inch floppy disk
and return postage. A users' manual covering design and use of both the PC and
CoCo software comes with the code.

   While neither the CoCo nor the IBM-PC TDDs requires a modem, it is necessary
to couple the computers to the phone line. Mr. Spalding's way of doing this is
with a Radio Shack telephone amplifier. Design details on this are available
from HEX, if you're willing to modify the amplifier according to instructions.
If you prefer to get your equipment ready to plug in, the modified amplifier is
available from John Steele, 2100 North New Road, Waco TX 76707. It plugs into,
and can be used with, either the CoCo or IBM-PC  using the Spalding software.

   Mark Becker has developed a program for the Altair 680b using the 6800
microprocessor which is intended to be used for radio teletype. It provides
conversion between ASCII and Baudot, and can be adapted to permit other
6800-series machines to work as TDDs. It is also in the public domain, and is
in INFO file C3.

   Conversions for the Apple, TRS-80 model I, Atari 400, Pet, Smoke Signal
Chieftain 6800 and 6809 machines were done by  various members of AMRAD, the
group which sponsors the HEX.  Design information and software for these are in
the public domain and can be obtained for the price of reproduction and mailing
(roughly 12 cents a page) from AMRAD's Corresponding Secretary, Howard F.
Cunningham. He may be reached at:

   AMRAD
   P.O. Drawer 6148
   McLean VA 22106-6148


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>>>>>>>> PURPOSE OF HANDICAPPED EDUCATION EXCHANGE ( HEX BBS ) :

---The Purpose of HEX---

   The Handicapped Educational Exchange (HEX) computer system was developed
under a grant from the U.S. Dept. of Education, Office of Special Education.
It serves two functions:

   1. It is a clearinghouse for information regarding the use of
microcomputers, and other modern technology, to aid the handicapped.
Information provided by users, and gleaned by the operator from technical
literature and personal correspondence, is entered into the files and made
available to anyone having an interest in this field. We welcome news of work
in progress, as well as advertisements for services and devices related to
the handicapped.

   2. It serves as a demonstration of the use of microcomputers to provide a
message system for the deaf. While there ate hundreds of computer bulletin
boards in this country, there are, to my knowledge, only three
microcomputer-based boards which are capable of being accessed by the deaf
using a TTY. The HEX  serves a number of deaf users, who employ it as a means
of exchanging messages and information of mutual interest. The technology
employed in the HEX is readily reproducible by anyone interested in providing
a similar service for deaf communities elsewhere. Information is available
from the
operator.


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>>>>>>>>>>> ASCII / BAUDOT CODE CONVERSION :

>>> send.c -- from the code for pc-hex tdd-=compatible bbs system.

              provides ascii/baudot code conversion

              copyright 1990 richard barth, all rights reserved.

              questions, comments and suggestions to:
              handicapped educational exchange (hex)
              11523 charlton drive
              silver spring md 20902

              bbs: [phone] (tdd and 300 baud ascii)
                         593-7357 (300/1200 baud ascii only, 8n1)
<<<

/* baudot code constants used for tty communications */

#define ucase    0x20  /* upper case flag     */
#define lcase    0     /* lower case flag     */
#define ushift   0x1b  /* upshift character   */
#define dshift   0x1f  /* downshift character */

static int  shift;     /* =ucase if a tty caller is in uppers, else =lcase */

____    ____    ____    ____    ____    ____    ____    ____    ____    ____

** these routines convert ascii to baudot and transmit it, and translate a
   received baudot character to ascii.

   the uart must be initialized for the correct word structure (5 data bits,
   1.5 stop bits, no parity, 45.5 baud) by the calling program.

   following is a table of ascii characters in the order in which they occur
   in the baudot code. certain baudot characters which do not exist in ascii
   are represented by nulls. the baudot null (all zero) character is normally
   used as a backspace on ttys, and is so represented in this table.

   note that while several variations of the baudot code exist, this table
   follows the "military standard" version used by the tty.
**

TABLE CONTINUED:____    ____    ____    ____    ____    ____    ____    ____

tatic
char bdotbl[]= { '\b', 'e', '\n',  'a',  ' ',  's',  'i',  'u', /* lower case */
                 '\r', 'd',  'r',  'j',  'n',  'f',  'c',  'k',
                  't', 'z',  'l',  'w',  'h',  'y',  'p',  'q',
                  'o', 'b',  'g',   0 ,  'm',  'x',  'v',   0 ,

                 '\b',  '3', '\n', '-',  ' ',   7 ,  '8',  '7', /* upper case */
                 '\r',  '$',  '4','\'',  ',',  '!',  ':',  '(',
                  '5', '\"',  ')', '2',   0 ,  '6',  '0',  '1',
                  '9',  '?',  '&',  0 ,  '.',  '/',  ';',   0   };


TABLE CONTINUED:____    ____    ____    ____    ____    ____    ____    ____

baudout(c)       /* convert ascii to baudot and send it */
int c;
{
    int i;

    for (i = 0;  i < 64; i++)   {
         if (bdotbl[i] == c) {   /* if character is found in the table */
              if ((i >= 32) && !shift) {     /* if needed, send shift  */
                   while (com_writ(ushift)==0)    /* char and set flag */
                        ;
                   shift = ucase;
              }
              else if ((i < 32) && shift)   {
                   while (com_writ(dshift)==0)
                        ;
                   shift = lcase;
              }
              while (com_writ(i)==0)        /* send baudot character   */
                   ;
              return (i);                   /* and return its value    */
         }
    }
    return (-1);                            /* if not found, return -1 */
}

TABLE CONTINUED:____    ____    ____    ____    ____    ____    ____    ____

b2a(c)           /* translate a baudot character to ascii */
int c;
{
    c &= 0x1f;                      /* mask to 5 bits  */
    if (c == ushift)  {             /* process shift characters    */
         shift = ucase;
         return (0);
    }
    if (c == dshift)  {
         shift = lcase;
         return (0);
    }
    c = (c | shift);                /* mark others for proper case */
    return (c = bdotbl[c]);         /* convert to ascii and return */
}

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