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RBBS in a Box Volume 1 #3.1
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RBBSIABOX31.cdr
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pcpo
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pcpgplot.fix
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1984-12-06
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A p p l i c a t i o n N O T E
Date: November 12, 1984 From: Chris Bradley
Product: Personal Computer Picture Graphics system
Hewlett-Packard 7470A two-pen plotter
There has been a great wailing and gnashing of teeth over getting PCPG to
draw its pictures on plotters. The main menu of PCPG offers to do this, as
well as digitize points coming FROM a plotter. but makes no description of
how to configure the plotter to receive data from PCPG. I cranked on this
for a couple hours, and this is how you can get it to work.
PCPG opens the plotter as a communications file (it's written in compiled
BASIC) with the configuration "COM1:2400,S,7,1,RS,CS65535,DS,CD". This means
that the plotter ought to be set up for 2400 bps operation, with SPACE parity
and 7 databits. BUT! the HP 7470A will not support SPACE parity, and so a
patch is necessary.
For you programmers, the patch is to change the byte at [CS+100H]:FC78 from
53H to 45H. If you don't understand that, then you can patch the PCPG code
like this:
1) Rename the PCPG.EXE file to something innocuous, like
P.XXX
2) Get the IBM debugger, DEBUG.COM, into the same directory
as P.XXX
3) From the DOS prompt, enter <debug p.xxx> and press return.
You will see disk activity, then you will receive a dash
prompt (-) from DEBUG
4) At the "-" prompt from DEBUG, enter <rcs> and press return.
You will receive a four-digit hexadecimal number, in the form
of "XXXX", then a colon (":") on a new line. Take this number
and add 100 to it.
examples:
-rcs -rcs
4912 3617
:4A12 :3717
- -
5) After changing CS, enter <e cs:fc78 45> and press return.
6) Save your changes by entering <w> and return.
7) Then, enter <q> and press return to quit DEBUG.
8) Rename P.XXX back to PCPG.EXE
At this point, PCPG is modified to use 2400 bps, 7 databits, even parity,
and 1 stop bit. The normal IBM-HP7470A cable will work. Set the switches
on the 7470A plotter like this:
+------------------------------------------------------------+
| 1 | | | 4 | 5 | | | | on or "1"
|------------------------------------------------------------|
| | 2 | 3 | | | 6 | 7 | 8 | off or "0"
+------------------------------------------------------------+
That's it, enjoy - you read it first on DalTex FIDOnet.