20 Feb
2004
20 Feb
'04
8:56 a.m.
Witchy wrote:
Get one of those cheap RS-232 status monitors (just has LED's
on several intresting signals) that are powered by the interface.
They make diagnosing most problems easy, and don't require
you to carry batteries around.
Put it in line with the cable, and see if both Tx and Rx light up.
If both light up, your cable is probably Ok, or you really really
botched the cable.
If only one lights up, try unplugging each side and see if both
sides are lighting up the same wire (Tx or Rx). If they are, you
need a "Null Modem" (or just swap Tx with Rx and DSR with
DTR).
Of only one side is lighting it up, then you have a problem
external to the cable.
-----Original
Message-----
From: cctalk-bounces(a)classiccmp.org
[mailto:cctalk-bounces@classiccmp.org] On Behalf Of R. D. Davis
Sent: 20 February 2004 04:56
To: cctalk(a)classiccmp.org
Subject: VAX console and crossover cable problem
MMJ DB25
DTR 1 ---- 6, 8 DSR, DCD
TX+ 2 ---- 3 RD
TX- 3 ---- 7 Sig Gnd
RX- 4 ---- 7
RX+ 5 ---- 2 TD
DSR 6 ---- 20 DTR
----------- MMJ pinout I'm using,
1 2 3 4 5 6 - viewed from
-------+ + console
+--+
Any ideas as to what I'm doing wrong? Didn't use my breakout
box yet, since I need to get new batteries for it.
My wiring bible built up over many moons has a passive
MMJ-DB25 pinout as
the reverse of that based on your diagram above:
1 - 20 DTR
2 - 2 Tx
3 - 7 TxG
4 - 7 RxG
5 - 3 Rx
6 - 6 DSR
That's what I'd use to make up a connector cable.
Cheers
Note: I've seen many MMJ cables/bulkheads ignore 1 and 6.
Since the VAX usually uses XON/XOFF, this isn't usually a
problem. It's usually happy having just 3 wires: Tx, Rx,
and gnd (TxG+RxG).