LA36 various responses

From: Don and Jose Woods <alderney_at_telusplanet.net>
Date: Fri Dec 27 18:19:06 2002

One person interested in 20 ma LA36's, and I think an answer in error from
Don Maslin. Thanks for the information on the 20 ma question Kevin and Larry

I'm not sure if these units are 20ma loop - but from their history I'd
expect them all to be the same. The plug on the connecting cable is a DB25
female, and the wires go to pins 1 through 7. Models are; Datacom 400 (the
one which may work), 2 Datacom 1200's, and 1 Decwriter III. Does the pin
connection help with the 20ma question, or is there a simple test I can make
on the lines? I'm not sure from Kevin Hardy's letter if one could just
change the wiring - it sounds like it, but these may be OK already. I tried
to see if I could tell what the output driver is (as per Larry's comment),
but the board isn't very easy to see. There appears to be an output IC
labelled 7550 - is this a valid TTL number?

Don Woods

Message: 3
>From: Barry Moyer <barry.moyer_at_pason.com>
>To: "'cctalk_at_classiccmp.org'" <cctalk_at_classiccmp.org>
>Subject: DEC LA36
>Date: Tue, 24 Dec 2002 09:08:19 -0700
>Reply-To: cctech_at_classiccmp.org
>
>Don,
>
>I am in Calgary and I have a newer LA36, but I am looking for another older
>LA36 with a 20mA loop connection. You can contact me at 'iamvirtual at
>hotmail dot com' (replace at with _at_, dot with .)
>
>Thanks
>
>Barry
>
...
>
>Message: 9
>From: "Fred Flintstone" <iamvirtual_at_hotmail.com>
>To: cctalk_at_classiccmp.org
>Subject: Re: DEC LA36 units
>Date: Tue, 24 Dec 2002 10:46:02 -0900
>Reply-To: cctech_at_classiccmp.org
>
>Don,
>
>I am currently looking for an older LA36 which has a 20mA connection (I need
>it to connect to my ancient PDP-11s). Do you know the model numbers for the
>LA36?
>
>Thanks.
>
>--Barry
>
>.
>
>Message: 15
>Date: Tue, 24 Dec 2002 15:59:09 -0800 (PST)
>From: Don Maslin <donm_at_cts.com>
>To: cctalk_at_classiccmp.org
>Subject: Re: DEC LA36 units
>Reply-To: cctech_at_classiccmp.org
>

>No Barry, sorry, but Dec printers are outside my area of knowledge.
>
> - don
Message: 4
Date: Thu, 26 Dec 2002 09:39:19 -0700
From: Kevin Handy <kth_at_srv.net>
To: cctalk_at_classiccmp.org
Subject: Re: DEC LA36
Reply-To: cctech_at_classiccmp.org

Barry Moyer wrote:

>Don,
>
>I am in Calgary and I have a newer LA36, but I am looking for another older
>LA36 with a 20mA loop connection. You can contact me at 'iamvirtual at
>hotmail dot com' (replace at with _at_, dot with .)
>
>

I believe that the 20ma current loop was available for all the LA36's.
It was just a different cabling option, bit a 'new' or 'old' version thing.
You could buy the 20ma current loop with your LA36, or later as
an option to change an existing one from RS232 to 20ma.

Message: 13
From: "Truthan,Larry" <truthanl_at_oclc.org>
To: "'iamvirtual_at_hotmail.com'" <iamvirtual_at_hotmail.com>
Cc: "'cctalk_at_classiccmp.org'" <cctalk_at_classiccmp.org>
Subject: DEC LA36 Decwriter II
Date: Thu, 26 Dec 2002 16:42:02 -0500
Reply-To: cctech_at_classiccmp.org

I have the engineering prints in the LA 36 Decwriter II

LA36 (MPC5) sheet 5 of 8 shows 20 ma RECIEVE on J3 pin 7(+) and Pin 3(-)
bridged by a 3.3 volt zener D4 746A feeding a 4N26 (E43) opto-isolator
which drives a MXAA05 (Q4) driver transitor which has its collector on J4
pin 2 "S.I." (serial in)

20 ma TRANSMIT is on J3 Pin 5(+) and Pin 2(-). These pins are bridged
by a 1N4004 diode D6. This diode also is parallel to the
emitter/collector of Q2, an A05. which is driven by another 4N26
opto-isolator (E47). S.O. is J4 pin 4. It is driven by a 7404 inverter
(E62)-(Input is 7404 pin 3 connected to the diode cathode of the
opto-isolator, output is 7404 pin 4, which connects directly to J4 pin 4,
"S.O." serial out)

Sincerely

Larry Truthan
Received on Fri Dec 27 2002 - 18:19:06 GMT