DEC LA36 Decwriter II

From: Frank Arnold <>
Date: Sat Dec 28 17:36:42 2002


>From: "Fred Flintstone" <>
>Subject: Re: DEC LA36 Decwriter II
>Date: Thu, 26 Dec 2002 13:43:54 -0900
>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.

Ok, you seem to have a third party controller in your LA36. Because DEC build a
real heavey-duty construction for the LA36, and let it print only with 30 cps.
many people and some companies thought it could do much better.
The few companies mentioned before put to the market several replacement-
controllers, making a LA36+ (mpnc) with a much better performnce, sometimes 150
or so cps, loadable fonts and/or pixel-graphics ect. The many people bought
those controllers and integrated them into their LA36'es and DEC-Fieldservice
didn't got tired of telling anyone that a terminal upgraded that way would
certainley disintegrate into its atoms "whitin months"... (I've never seen this
These 3rd-party controllers would completeley replace the original DEC-made
logic board that was attached to the innerside of the back-door, and was about
just as big as that door itself.

(mpnc = my personal naming convention)

So the DEC printset won't help you much with this, you should find a manual of
Datasouth, to get details on the dip-switches. (most likeley they set the
baudrate, and the switch in the keyboard has maybe got some other function.

>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.

That should be possible, 11/10+05 have only 20mA cuircuits. The 11/05 computer
is always the active party (=supplying current to the loop) on both Tx and Rx.
The baud-rate is made by a rather unstable pair of one-shot monostables. Use a
osscilloscope to set the time of this to either 26 or 35,5 microseconds.
You need 26 us for the selection of 150 (tap5) - 2400 (tap1) baud, or 35,5 us
for 110 baud on tap5 of the swich.

>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

I think, thats normal, afterall when the terminal is idle, there will be no
current flow. Put your multimeter into mA-mode, and put it in series into the
loop. Use preferably a cheap passive arrow-meter, the cheaper it is, the better
the measurement. Alternativeley, you can also put a led somewhere in the loop.
create data-output, and see what happens

>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.

Seems ok to me. (long time ago...)
(Beware however that the naming-conventions for ths 20mA current-loop were not
always consistent. There is no industry standard for this. I dont know how
Datsouth has named its connection-terminals)
If all this is ok, still nothing will happen if the baud-rate is unmatched
between 11/05 (rotary switch and trim-potentiometer on M7260) and probably
dip-switch and/or Keyboard-button or keyboard sequence 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 mode.


Hope you can solve this.

Received on Sat Dec 28 2002 - 17:36:42 GMT

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