29 Feb
2020
29 Feb
'20
5:40 a.m.
Most of the RS232 spec seemed to be designed for Sync modems and their management.
Most machines of the mini generation seemed to use either Async or Sync interfaces. Stuff
like the VT180 had a comm port that was a 8251 USART for serial comm that could be either
sync or async. I don't believe Dec had anything like that in that PDP11 or early Vax
days.
Anyone care to enlighten me?
Bill
Sent from pechter(a)gmail.com
-----Original Message-----
From: Clem Cole <clemc(a)ccc.com To: William Pechter
<pechter(a)gmail.com Cc: Computer Old
Farts Followers <coff(a)tuhs.org Sent: Fri, 28 Feb
2020 17:36
Subject: Re: [COFF] 52-pin D-Sub?
below...
On Fri, Feb 28, 2020 at 5:26 PM William Pechter <pechter(a)gmail.com> wrote:
Could it be because they all started with current loop
tty interfaces?
Most of the old DEC guys started with teletypes.
Very possible...
Having struggled with a breakout box and different mini and micro vendors
implementations of serial ports... Ugh. And in three-wire the use of
Xon-Xoff varied big time. No standard was the standard. IIRC the IBM
Series/1 had a different 9pin layout than the PC/AR. Why?
RS-232A/B/C was DB-25 P for the DTE (terminating equiment - a.k.a.
terminal) and S for DCE (communications equipment - a.k.a. modem). It was
standardized. At one time, I (sadly) could quote the paragraph number....
Then in 1978 #$%^& Lear Seglier put a DB-25S on a DTE (terminal). They
were the cheap terminal vendor and all hell broke loose.
The PC/AT used 9 pin because the back of the unit was small and -- well
there could because IBM said so .... But at least the IBM engineers kept
to Plug and Sockets from the standard. I did not know the Series/1 used 9
pin. Learn something new.
At least DEC was reasonably consistent until they
moved too the Vax
modified RJ design.
Indeed - that was a huge issue - the modified RJ block -- sigh...