DEC VT05 with OS/8 -- basic system rebuild?

Johnny Billquist bqt at
Mon May 18 13:15:35 CDT 2009

Rick Murphy <rick at> wrote:

> At 05:17 AM 5/17/2009, Johnny Billquist wrote:
>> Chris Elmquist <chrise at> wrote:
>>> I may have missed some facts earlier in this thread--  but does the 
>>> system
>>> obey hardware flow control such as CTS?  ie, if CTS is low, will it be
>>> blocked from transmitting?   If that is obeyed by all of your OS and
>>> software, then it is not hard to build a microcontroller that would sit
>>> between the system and the terminal, adding the delays you need on <cr>
>>> while buffering for and hardware flow controlling back toward the PDP-8.
>> In general, when talking about DEC equipment, the answer to that 
>> question is *always* no, for the simple fact that DEC didn't do 
>> hardware flow control. Hardware flow control is actually against the 
>> RS-232 spec, and DEC didn't abuse standards (unlike most other companies).
> And, of course, there's a pretty good chance that this VT05 is 
> connected via 20ma, not RS232.
> (Assumption based on the fact that there's an easy fix in the KL8-JA; 
> given that this hasn't been used to fix the problem, it's probably not 
> an omnibus computer. Pre-8/E serial devices were often current loop.)

Assumption wrong. :-)
The original posted have a KL8-E, which is software compatible with the 
KL8-JA, but don't have the filler fix that the KL8-JA have.
They are both omnibus devices.
The KL8-E is actually kindof cool, since it implements a UART in 
discrete logic. One side effect of that implementation is that you can 
send a break character, since the transmit shift register is always 
loaded immideately, even is a character is currently being transmitted, 
and the stop bit is also shifted through the register, thus you can 
"overwrite" the stop bit with additional data.


Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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