Altos ACS 8000-15A

Ethan Dicks ethan.dicks at
Sun Jun 14 16:00:19 CDT 2015

On Sun, Jun 14, 2015 at 3:47 PM, Chris Osborn <fozztexx at> wrote:
> ,,, Altos ACS 8000-15A... nothing spits out on the Console 1 RS232 port. From
> what I understand the serial ports are wired DTE (which seems odd since you
> use it with terminals) and so I’m using a null modem adapter. Although with
> the null modem or without I get nothing.

I wouldn't assume anything with serial ports, especially vintage ones.
Look into getting a "traffic light" that displays state on LEDs either
in red or red/green (depending on how old/expensive the traffic light
- I have both kinds).  The "easy" way to sniff out a connection with
one is to plug the traffic light into only one side of your connection
and see which lines are active, then unplug that and plug it only into
the other side and see which lines are active.  If you have your
null-modem/no-null-modem swaps right, the active lines will be
complementary on each side.  If, say, RxD is active on both, you'll
need a null modem.  When you have it right, you should see lights
blink when one side or the other is trying to talk.  Choosing a baud
rate slower than 9600 bps makes it easier to see.

Also, some hardware needs hardware flow control present and working.
Newer stuff is fast enough that mostly, people just do 3-wire serial
(RxD, TxD, and GND), but stuff from the 1970s is expecting CTS and RTS
and all that to do the proper things.  Sometimes, you can just wire up
the computer side to always have CTS active and things will work fine
since the computer/terminal side can keep up and doesn't have to
throttle one character at a time.  Frequently, this requirement can be
enabled/disabled with jumpers or software settings on the computer
side, but if not, you might need a custom console cable.

This is part of the joy of serial comms.  If you aren't used to
debugging line speeds and parity bits and null-padding chars and
hardware handshake lines, it can get very frustrating when you try to
connect two devices and they won't talk.  By the mid-90s, when most
serial comms were relegated to various types of modems, many of the
earlier limitations were no longer important, but the further back you
go, the more parameters you had to get right before traffic flowed.


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