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ORIGINALLY PUBLISHED IN LIMA NEWSLETTER JUNE 1993

      LIFE WITHOUT THE HEXBUS, or
     HOW TO USE A CGP-115 4-COLOR PLOTTER ON THE TI-99/4A
     by Joseph Cohen
     Lima Ohio User Group

     We have heard many times about those wonderful things we COULD HAVE done
with our TI-99/4A IF only we had the hex-bus interface, that little item
listed, I believe, for about $60 by TI in late 1983.  With it you could attach
-and use- the hexbus peripherals to your TI-99/4A.  (Ed. note: For a complete
description of the hex-bus interface see the April 1993 issue of BB&P, the Lima
newsletter.)

     It so happened that the hex/bus interface was never marketed after all,
and only a handfull of units are in existence mostly as collectors' items.
Certainly that does not encourage any of the regular TI-99/4A users.  On the
other hand, some of the hexbus peripherals themselves were released and
marketed for the CC-40.  Reviews of most of these peripherals have been
published by Charles Good in Bits Bytes and Pixels (BB&P) - the Lima Ohio User
Group newsletter. (Ed. note: Anyone can obtain the complete set of articles in
DV80 format by sending two DSSD disks and a paid return mailer to P.O. Box 647,
Venedocia OH 45894.)

     Well, all is not lost.  for one thing, some of these peripherals are
mostly of historic value.  The wafertape drive, for example, was fine as an
inexpensive alternative to a disk drive.  Back in 1983, when disk drives were
very expensive, this was important.  However nowadays, with prices of expansion
boxes heading down, it is no longer necessary.  As an aside, it is interesting
to note that the Adam computer (another orphan, with a TI video chip!)
originally came our with a wafertape drive.  It is my understanding that
practically all serious users have upgraded to real disk drives.  There were
also wafertape drives designed and sold for the Radio Shack TRS-80 and the
Commodore Vic-20 (ok, ok, the computer wars are over since 1983!) and C-64;
they never got too popular, to say the least.

     A really handy and useful hexbus peripheral was the 4-color pen
printer/ploter HX1100, reviewed in the October 1983 issue of 99'er Home
Computer Magazine and more recently in the January 1991 issue of BB&P (Volume
7, number 1).  This little device was capable of both text and graphics modes.
In the text mode it would write in 40 (regular size) or 80-(tiny letters
characters per line.  In the Graphic mode it could plot in four colors using
little pens.  It was fully programmable from BASIC and capable of plotting
mathematical equations including the axes and using different line types
(solid, dashed, dotted, etc.), business graphs (pie charts etc.) in color,
3-dimensional drawings, and much more.  Text in the graphics mode could be in
ANY size and in ANY direction (e.G., sideways, upside down, and so on) so it
could be usefull for preparing little posters and name tags, among other
things.  Pen color was fully controlled and could be changed at any stage
during the program.

     Sounds like a big loss, doesn't it?  Well, all is not lost!  Atari was
marketing a very similar device, called the 1020 printer/plotter, for their
line of 8-bit computers.  I understand that those are readily available in
practically unlimited quantities from atari 8-bit dealers, but they use the
special Atari interface that is difficult, if not impossible, to adapt to the
TI.  However, if anybody knows how to do this, here is the information on the
availability of such units.  For the rest of us, though, there is a better
solution - the Radio Shack TRS-80 CGP-115 printer plotter.

     The CGP-115 was described in the April 1985 issue of Mini-Mag 99, a short
lived TI-99/4A related publication.  the article contains a detailed
description of hooking it up to the TI-99/4A and numerous short TI BASIC
programs that produce amazing results on the printer plotter.  More examples
are given in the radio Shack manual.  If you try to run those programs on your
regular printer, you will only get lines full of ASCII characters, but the
CGP-115 has built in graphic commands that respond to these programs.  As a
result, very simple and short BASIC programs will produce beautiful plots.
(Some sample plots are shown with this article.)

     The CGP-115 ROM contains, among other things, the following commands: (i)
establish the origin and send the pen to this origin at any time; (ii) move the
pen, with or without drawing, between specified points; (iii) move the pen,
with or without drawing, from the established origin to any desired point on
the paper; (iv) choose between the four pen colors; (v) select any of 16(!)
line types; (vi) write text in graphics mode from 1/16 of an inch high
characters up to 4 inch ones in 64 steps between these sizes; (vii) select text
printing direction in graphics mode; (viii) shift freely between text and
graphics modes.

     In text mode the CGP-115 produces superb 40 or 80 characters per line
letter quality output, in any of the four colors, at 12 cps.  Since the paper
is about 3.8 inch wide, the 80 character per line text is written in very small
letters, however they are perfectly readable.  The drawing resolution is 0.2
mm/step, and the results are really outstanding.  The graphics mode produces
high-quality plots of equations, all kinds of geometric shapes, pie charts,
business graphs, and your own designs!  The plotter is small and compact.  The
effective plotting range is 3.8 inch wide (fortunately this is larger then the
HX1000 paper!), and the weight, without paper pens and the power transformer,
is 1.76 lbs.  The device is highly mechanical: drawing involves pen movement,
pen holder rotation to change colors, and a lot of paper movement in and out of
he plotter to achieve lines in the y-direction (the pens move along the
x-direction, while the paper moves along the y-direction).

     The CGP-115 interfaces directly with the TI-99/4A.  I have not seen the
hexbus printer/plotter, but it seems that apart from the interface, the only
diference between this and the HX1000 unit is the power supply and paper size
(the CGP-115 uses wider paper).  The Hex-bus unit was powered through a
rechargable battery, and according to the BB&P article this is actually a
disadvantage.  The Radio Shack unit is powered through a DC transformer (you
might be able to build your own battery holder and power it this way if you
like).  The interface is somewhat of a problem though.

     The CGP-115 has two interfaces.  The parallel 8-bit interface uses BUSY
handshaking, STROBE, and AACKNOWLEDGE, and it is suitable for use from the
TI-99/4A PIO output from the RS232 PEBox card.  However, like all other Radio
shack, Okidata and a couple of other printer models, this interface requires
the so-called Okidata parallel printer cable to operate (this cable corrects
som timing  problems in the 99/4A PIO).   What this means is that, if you are
using a printer that does not require the Okidata cable (and most printers fall
under this category; e.g. Epson, Panasonic, Star/ gemini), you will need
another cable.  (Ed. note: The "Okidata" parallel printer cable for the TI
RS232 card is inexpensively available from Competition Computer; 800-466-8902.)
I suggest the CGP-115's serial interface.  If the parallel interface is your
choice, you can still use it and leave your regular printer attached if you
have in your PEBox a secpmd RS232 card (i.e., PIO/2) with the Okidata cable.
It is also possible that that more standard 3rd party parallel outputs will
work better, and this is left for the user to check.  another attractive
possibility is to use a serial-to-parallel converter.  These small devices will
ake a serial output and convert it to parallel.  they are attractive because
every RS232 card has two built in serial outputs, and unless you have got a
modem or a serial printer, you are not using any of them!  Also, the converter
usually has a printer buffer built into it, and this is helpful as the CGP-115
(and any plotter) is rather slow and unless you have a buffer you will have to
wait while it is plotting.  The serial-to-parallel converter/buffer would
usually accept inputs at very high speeds (up to the maximum of your RS232
output, 9600 bps) into its RAM, and your computer will be free very quickly.
It is also handy when you need multiple copies of the same plot.  Incidentally,
such a device is also useful with cartridges that only print to the serial prot
(RS232) when your printer has a parallel interface.

     Perhaps most users who will try using this plotter will end up hooking it
up through its serial port.  The Radio Shack TRS-80 serial port uses a round,
4-pin DIN serial connector with DATA and BUSY signals.  The CGP-115 operates at
600 baud, 7-bit character, no parity, 2 stop bits.  there is no problem with
this slow baud rate, since the unit itself is rather slow, and TI BASIC is even
slower.  as pointed out in the Mini-Mag 99 article, the required connections to
he TI-99/4A RS232/1 port are:
     CGP-115 male DIN PLUG^^^^TI99/4A male DB25 plug
     PIN 1------------------------> No connection
     Pin 2------------------------> Pin 20
     Pin 3------------------------> Pins 1 and 7
     Pin 4------------------------> Pin 3
     The CGP-115 can now be OPENed as RS232/n.BA=600 where n=1,2,3, or 4
depending on your system configuration.

     Don't rush out to the nearest Radio Shack to but this unit, as the TRS-80
line has long been discontinued and you won't find it there.  If, however, you
are lucky enough to find a used one, Radio Shack still sells the paper and pens
for it.

     I am grateful to Charles Good for showing me his copy of Mini-Mag 99,
where I have found all about this device.  If anybody out there has a copy of
th second part of the article, I'd like very much to see it!  I would
appreciate any help on this.  and finally, if you proceed to hook up this
device to your RS232 card, you are doing so at your own risk!  I take no
responsibility for any of the consequences, good or bad!
     .PL 1