DEC VT05 with OS/8 -- basic system rebuild? - test-drb@ccmp.vtda.org

18 May 2009

Rick Murphy <rick at rickmurphy.net> wrote:

...
  At 05:17 AM 5/17/2009, Johnny Billquist wrote:
  Chris Elmquist <chrise at pobox.com>
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

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