DEC LA36 Decwriter II

From: Fred Flintstone <>
Date: Thu Dec 26 16:41:00 2002

I guess I should have been more specific :-)

I have what appears to be an OEM LA36. The label on the front says 'Data
Terminal Mart'. On the back, there is a label from Digital which gives the
model number as LA36DP. The processor board inside is made by Datasouth
Computer Corporation (P/N 512000-2). There is an 8 DIPswitch located on the
board. I do not have any documentation for this particular model and thus,
I do not know what the settings should be on the switches. I do have user
docs for an older LA36, but it does not cover my particular model.

I am looking for information on the LA36, specifically the 8 dip switches.

What I am trying to accomplish is to get the terminal console working on my
PDP-11/10 (really it is a PDP-11/05) prior to getting my PDP-11/20 running.

When I hook everything up, the SCL on the PDP-11/10 has the expected
voltages. When I connect it up to the LA36, the voltages are driven to near
0v. I am not sure I have things hooked up correctly, or if there is a
problem with the SCL. I used the docs I had for the older LA36 to connect
my LA36DP. The connections I made were from T+ on the PDP-11 to R+ on the
LA36 and T- on the PDP-11 to R- on the LA36. When the LA36 is not
connected, there is no voltage on the Transmit/Receive which I am presuming
means the LA36 is in passive mode. Voltages are present on the
Transmit/Receive on the PDP-11 side, and I presume the SCL is in active

Unfortunately, I am not sure if this is correct (I am from the RS232
generation, the 20mA is slightly confusing).

Any ideas?

>From: "Truthan,Larry" <>
>To: "''" <>
>CC: "''" <>
>Subject: DEC LA36 Decwriter II
>Date: Thu, 26 Dec 2002 16:42:02 -0500
>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
>(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)
>Larry Truthan
>In reply to:
>Message: 29
>Date: Thu, 26 Dec 2002 09:39:19 -0700
>From: Kevin Handy <>
>Subject: Re: DEC LA36

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Received on Thu Dec 26 2002 - 16:41:00 GMT

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