20 Oct
1999
20 Oct
'99
6:28 a.m.
-----Original Message-----
From: allisonp(a)world.std.com <allisonp(a)world.std.com
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu Date: Wednesday,
October 20, 1999 2:09 PM
Subject: Re: OT: how big would it be?
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
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