[SOLVED] Trouble interfacing via RS-232 with HP 54600 series oscilloscopes

[iroc86]

I'd like some help getting an RS-232 connection to work with my HP 54645A oscilloscope and HP 54659B interface module. No matter what I try, the device won't output any data through the serial port. I'm testing the connection using the Print Screen function in the Print|Utility menu on the scope. Although my serial console (PuTTY or Termite) isn't a printer, I'd expect to at least see some traffic on the line. I'm also unable to receive responses for commands that I send according to the Programmer's Guide [pdf], such as a basic *IDN? query.

I'm using a genuine FTDI USB-to-RS232 adapter (Chipi-X10) and have verified with a loopback connection that the device works. For the scope, I've tried no less than four different variations of null modem cables based on HP's documentation and other websites that discuss interfacing with the 54600 series (attached below). I've also tried different handshaking methods; XON/XOFF and DTR/DSR. Nothing has worked. I can see the indicator lights in my serial console change based on the cable and handshaking mode, but that's about it.

Has anyone encountered this issue before? I'm no stranger to RS-232, but I've never seen a device that's been so stubborn to connect. Based on the difficulty, I'm probably missing something incredibly simple or stupid.

[TK]

From the 54659B 54658B manual

[iroc86]

TK, those diagrams are for the 54658A, which has a DB-25 connector. My module is the 54659A, which has a DE-9 connector. The pin mapping is the same, though. Page 1-7 of the 54659A manual [pdf] only shows one pinout for the DE-9 connector, which is the upper right diagram in my post ("RS232-61601 Cable"). The other one came from here: https://www.keysight.com/main/editorial.jspx?ckey=558637&id=558637&lc=eng&cc=US

[TK]

Sorry I didn't know there was a DE9 interface.  I can try printing on mine and see if the scope outputs any information on the RS232 pins.

[elecman14]

I would try and get the ke5fx plotter software working to verify that the plugin is working. Here is a guide to doing that with that scope https://projectaweek.com/2018/07/01/using-ke5fx-hp-7470-plotter-emulator-with-a-54659b-module-on-a-54600b-oscilloscope/

[iroc86]

I appreciate the replies, guys. Yeah, the HP manual can be little confusing with the D-Sub connectors since they try to cover the 54657A, '58A, and '59B in a single manual. It threw me for a loop too, TK. Elecman14, thanks for linking in the ke5fx software--I was trying for the life of me to remember the name of that package!

Well, I managed to find the problem. As I expected, it was both simple and stupid, although at least it didn't have anything to do with me! You guys are going to love this one...

I took the scope into work today to test out some other RS-232 hardware and see if I could isolate the problem. The results were the same as before: no connection sending or receiving, weird behavior with the hardware handshaking pins, etc. My colleague suggested that we try to probe some pins and attack the problem from the hardware level, since nothing on the software side was helping. Per the 54659B manual, the DCD, DSR, and CTS lines are all held high by the scope via pull-up resistors. At the very least, those pins should be high... and only the DSR pin was.

Suspecting that maybe the RS-232 driver was blown or the pull-up resistors were fried, we took apart the controller to check things out. Can you find the problem in the picture below?





It only took a moment to figure out what was wrong. The damn DE-9 connector wasn't soldered in! This is a genuine HP expansion module that completely missed its quality control checks. In the close-up shot, it's clear that this wasn't a failed repair by an end user--those pads look freshly plated with no hint of solder or flux reside.





Needless to say, I'm glad this was an easy fix, but I'm amazed that this was the cause of the issue. I know these things happen from time to time on any production line, but more interesting is the "Instrument Tested" sticker on the back of the board. This thing was clearly a Friday afternoon job that slipped through the cracks.

At any rate, all is well now. I can verify that the plotter function does actually output serial data, I can control the scope remotely with the various programming commands, and I was even able to get an old version of Agilent IntuiLink to work under VirtualBox running Windows 2000. Sometimes the simplest of problems have the stupidest of solutions!