-----Original Message-----
From: allisonp_at_world.std.com <allisonp_at_world.std.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Wednesday, October 20, 1999 2:09 PM
Subject: Re: OT: how big would it be?
>On Wed, 20 Oct 1999, daniel wrote:
>
>> Allison: You worked on transistor 8s? How did they impliment the 20mA
>> current loop. I posted a message a while back about how it *was* set up
in
>> this cpu. The schematics of a PT08 show nothing other than one TTY line
>> right into the receiver board.
>
>It was a transistor level converter from logic levels to 20ma. the
>circuit for wich is fairly simple. It was the serial/deserial hardware
>that ate a few boards. As in the case of the most 8's the tx/rx data was
>directly to the Accumulator. There were designs that would stall the
>machine while the bits were serialized/deserialized and written one by one
>to Acc. Saved registers but the cpu was stopped for about 1/10th second.
>
>Allison
>
I know that but do you know the original circuit used between the teletype
and the receiver board? I have a simple circuit running now. The current
backplane shows R107 (inverters)
john
>
Received on Wed Oct 20 1999 - 13:28:24 BST