H89 as serial terminal

From: Patrick Rigney <patrick_at_evocative.com>
Date: Fri Mar 28 01:04:00 2003

> >much easier than any of the above... get a copy of MDM712 or similar
> >terminal emulation program. MDM712 comes with a serial port driver for
>
> Hi
> Why would you assume that finding and installing some
> software would be easier than making up a simple molex adapter
> connector. As I recall, it was a 9 pin molex but I could
> be wrong. That is all of 9 wires to deal with.
> Dwight
>

Dwight, you're absolutly right, the software is not always "easy" to find
and get. Actually, check that... it's really easy to find and get (Google),
it's just not as easy to get onto a Heath-format floppy so you can use it.

On the other hand, I think the software approach has its merits, especially
over the long haul. Using a terminal emulator is a more permanent solution
(IMHO) than cracking the case and swapping connectors around to reconfigure
the device as a terminal or computer. And, the terminal logic board
communicates with the CPU board at 9600 baud, so if you want a different
rate for the device you are talking to, the board has to be pulled and
jumpers/switches changed, and then pulled and changed back if you want to
use it as a computer again. The three-port serial card has software
configurable baud rates. The hardware approach will also not make it
emulate VT-100, which is part of what Jason had asked. And since many of
these programs can X/Y/Zmodem, getting other stuff onto the machine from
there forward gets a lot simpler.

While you, I, and others may feel quite comfortable mucking around with the
innards of the beast, perhaps (and I don't know one way or another for sure)
Jason or anyone else who might later read this thread in archives or digests
may be less comfortable or is just working up to it, and so other
alternatives are worth mentioning (IMHO). Tony's hardware solution is good,
but rerouting even one of those cables may require removal of the CPU and
terminal logic boards, since the interconnect and serial cables are
typically routed around the bottom edge of the two boards and fairly tight
once home. If you're going to go back and forth between terminal and
computer, maybe that's a bit much in the long run. Add to this that the
expansion boards and some of the other connectors attached the CPU board are
all unkeyed and thus notoriously easy to (re)install one pin off their
mating connectors, and this little accident can cause the kind of rapid deep
frying on the CPU board that will turn a wonderful H89 into a dumb terminal
permanently.

I'm into risk management and choices. That's all. I certainly didn't
intend any offense with my comment.

But since we're into options... to elaborate on your and Tony's path, the
terminal logic board's serial port is easily accessed from the rear of the
machine--remove the lid, and as you face the back of the machine, it's on
your left (you can sometimes read "P404" next to it). If a cable is the
solution of choice, then Molex directly to a DB-9 or DB-25 (whatever the
device to be connected requires) is the way to go, IMHO. That way, you can
just open the case, pull the interconnect, connect in its place this new
cable to the target device, and do your thing. Reverse to undo,
lather-rinse-repeat as needed. That won't get you VT-100, software
transfer, or other baud rates, but it is quick and dirty.

To that end, P404 on the terminal logic board is a 15-pin connector with 10
pins connected. For those interested, the pinouts are (from schematic w/no
revision number evident, identified Heath p/n 595-2268/595-2272):

1 - (black) ground
2 - no connection
3 - (brown) TxD
4 - n/c
5 - (red) RxD
6 - n/c
7 - (orange) RTS
8 - n/c
9 - (yellow) CTS
10 - n/c
11 - (green) DSR
12 - n/c
13 - (blue) ground
14 - (violet) DTR
15 - (grey) "RLSD/" (whazzat? anybody?)

The black wire (pin 1) is up in this vertical connector.

Patrick
Received on Fri Mar 28 2003 - 01:04:00 GMT