Serial analyzers (was Re: VAX 11/730 quickie)

Jay West jwest at
Tue Feb 23 21:50:07 CST 2016

Marc wrote....
 I was not sure what I would getting that a laptop with a good terminal
emulator and a serial port would give me. Can you convince me otherwise?
What do you guys use it for?
Perhaps there are terminal emulators out there that can do the following,
but I'm not aware of any that do these things that are the most common use

1) Display transmit on one line and receive on the other line, positionally
correct. Very easy to visually see what one side sent, and what the other
side replied.
2) Display the characters not just in ascii text, but in ascii mnemonics,
and better yet... binary, octal, hex. FAR easier to see what is REALLY being
transmitted and received. Ex - so if the unit is set to 81N, are the parity
bits right? You can tell visually at a glance without really thinking.
3) And given the display can be in binary, it's easy to see field values
that do not align on even count positions - ex: 8 bits where the first 3
bits mean something in the protocol, and the next field is 5 bits, etc.
4) Automatically trigger on events - ex. Watch the line until you see this
sequence from the DCE. Then insert this string as a reply, wait for this
response, then let the DTE continue. Oh, and start logging if this pattern
occurs 3 times.
5) Automatically calculate checksums by any one of a designated set of
algorithms, and verify the checksums being sent and received. Start logging,
up to 2K size, once a checksum mismatch occurs.
6) Run BERT tests to either side.
7) Often provide a breakout box to jumper and/or reroute wires.
8) Save data to a disk for later review, or print to paper.
9) Easily deal with async, sync, bsync, x.25, etc.

When writing your own communications protocols, a datascope makes
testing/troubleshooting a very quick process. The alternative ... not so

Many decades ago, I had a program for DOS (that I have since lost) called
"Breakout II". It came with a cable and required two serial ports. It was a
"software" breakout box. It was sorta handy... but it was no datascope.


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