BUGILES@UOFMCC.BITNET (DENNIS BRAMADAT) (01/02/87)
This is my first posting to Info_Amiga, so I hope you all will
forgive any faut pas that I may type. Thanks.
I recently bought a terminal emulation program (Gizmoz, from
Digital Creations) to enable me to talk to our VAX 750 via a
Develcon switch, and experienced some horrifying problems.
I started off by making the appropriate RS-232 connections to
the Amiga, and loading in the emulator program in VT100 mode
(Which doesn't seem to work very well at all!). I was then
able to get the switch's attention, but that was as far as I
got. No data whatsoever was being recognized by the switch,
but data was being accepted by the Amiga.
I played around with the various setting of the software package
for a long time, and after getting nowhere but frustrated, I
hooked a logic level monitor on the serial port of the Amiga.
As it turned out, the control lines from the switch were
sitting at reasonable logic levels and the Amiga lines were
ok in the logic 0 state (about +10Vdc). However, the logic 1
states originating from the Amiga were way under spec (about
-2.85Vdc). Standard RS-232 requires typical levels of +-12Vdc,
and I understand that the ABSOLUTE minimum requirements are
+-3Vdc.
After a little more testing, I realized that the Amiga was at
fault. I consulted the hardware manual, and to my astonishment,
I found that the Amiga serial drivers were being powered by a
-5Vdc supply. I was not impressed in the least! I'm not
sure, but I think someone mentioned that this was a common
practice of Commodore's. I expect that the marginal logic 1
levels will work just fine for short cable runs, but for long runs
of a few hundred yards, this is clearly unacceptable.
Since there is no -12Vdc power available on the Amiga, I ended
up building my own -12Vdc power supply, disconnecting pin 1 of
the MC1488 serial driver from the Amiga's board and connecting
up its new negative supply. With a little tin bashing, I even
managed to fit my power supply into the Amiga's case.
This whole procedure was kind of trying on my faith in Commodore
(several words were exchanged with imaginary Amiga designers),
and after the operation I promptly threw my warranty card in the
garbage. But I can now communicate with our VAX. The VT100
emulator does have some problems however, especially with the
arrow keys. Sound familiar?
At any rate, I thought I might mention this problem in light of a
recent digest posting regarding serial communications problems
with a MIDI interface - the symptoms sound all too familiar.
The whole project cost only about $6.00CDN. As an alternative,
I understand that there are commercial line drivers/level
converters available that would be a little safer to implement -
but not nearly as much fun!
As an aside, does anyone know where I can get an EPSON LQ-1000
printer driver? The generic Epson driver works for text, but
has difficulties with any sort of graphics. The Commodore
software people in Toronto were supposed to send one to my usual
Amiga dealer, but haven't responded yet (It's only been 4 months).
Thanks for putting up with my ramblings.
D.C.Bramadat
BU Physics
BUGILES@UOFMCC