25 Sep
2013
25 Sep
'13
11:46 a.m.
For my 8/L I made a very simple adapter card. I added a card at D33,
where normally there would be a W076 Teletype cable card. The card is
such that I can swap interfaces back to a real teletype, if needs be.
(Note: View in fixed font!)
The Transmitter portion:
I added a wire from the M707 C31D2 (TTL Serial out) to D33D1
+-----------+-------- +5V
| |
4.7K Ohm Collector
| .
D33D1 --- 220ohm ------+-------- Base Q1, PNP Silicon
.
Emitter ----- 47 Ohm ---+--- RS-232 OUT
|
3.3 K Ohm
|
-12V (Regulated)
I built a duplicate of the above for the reader flag. The input was at
D33E1 (My notes don't indicate if a wire had to be added, but looking
at the machine, there was, from D32L2 to D33E1) and the output was to
RS-232 Pin 5 (Clear to Send - CTS).
The -12V Regulated was derived thusly:
-15V (Mine measures at about -20V)
|
330 Ohm 1/2 Watt
|
+------------------ -12V (Regulated)
|
12V Zener Diode Anode
|
Ground (Zener Cathode)
For the RS-232 Receiver, I did the following:
RS-232 In ------------ 3.3 K Ohm -------+------------- D33E2
|
3.3 K Ohm
|
Ground
There is/was, apparently, already a wire from D33E2 to the M706 input -
that would normally carry the signal to a W076.
This simple circuit works, in part, because the TTY input board clamps
to 0V and +5V, so all I had to do was to limit the current drawn from
the RS-232 interface).
Adjusting the M452 clock (location C33) was a little tricky: Use a
'scope or frequency counter. I used 4800 bps.
Looking back on it, it is quit possible that the inputs I already needed
were on D33H1 and D33M1, so the wires I added may not have been
necessary, but I haven't looked at it real hard.
Jay
On 9/14/2013 7:19 PM, Josh Dersch wrote:
Hi all --
I'm attempting to get my 8/L talking to the outside world. It's
outfitted with the typical Teletype interface, which I'm attempting to
connect to a PC via acurrent loop to RS232 adapter.
Specifically, I've got one of these:
http://www.bb-elec.com/Products/Serial-Connectivity/Serial-Converters/Curre….
At the moment I have it configured (per the manual) assuming the 8/L is
an active loop device (i.e. the converter's transmit lines connect to
the 8/L's receive lines, and the 8/L's transmit lines connect to the
converter's receive lines). With this configuration I'm able to get the
8/L to send data to the PC successfully.
I'm not having much luck getting the8/L to receive anything from the PC,
however. If I put my multimeter in the loop, I see a current of about
40mA, which drops to between 30 and 37mA when the PC is sending data
(depending on what data's being sent). However, I'm not getting much of
anything onpin "E" of the W076 (Teletype Connector) board -- this is
supposed to be the "Logic Output" and I'm assuming that should be the
TTL-level data signal, correct?
I do see a very, very tiny signal (in the millivoltrange) on pin "E"
that matches up with the data being sent from the PC, but it's obviously
nowhere near the correct level. I've gone over the W076 board and
checked the related diodes and resistors for anything open/shorted. And
I actually did find a bad diode (fell apart when I desoldered one leg to
test) but replacing it made no apparent difference.
At this point I'm wondering if the loop configuration I have is
incorrect. I thought this was supposed to be a 20mA loop, but I'm
getting 40mA. I know very little about the fundamentals of current loop
stuff, so I could be way off here.
Anyone have any advice?
Thanks,
Josh