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Looking for suggestions on a 25-port oscilloscope (or DB25 monitor)

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voidstar78

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I'm working with an old system with a *pair* of DB25 connectors that aren't standard-anything (not RS-232). But, like RS-232, at least pin 1 is ground.

I have an 8-port scope, but it's getting "messy" trying to wire up that many individual BNC leads (mostly because of having to link up all the grounds). I get up to 4 or 5, then it's not much fun trying to monitor a few signals at a time (out of 48 other signals trying to see sychronous trends).


I suppose a pair of Arduino Mega's might be something to try for this? Not sure how fast that can read signals, but I think an individual Mega is 25+ GPIO pins. I think all the signals I'm looking at are 5v.


Does/did HP make anything for this? Something to just plug in a DB25 cable end, you designate which pin is ground (or go with pin 1 being ground), and from there it tells you any activity going on the rest of the pins? I'm not yet sure what resolution I'll need, that's part of the exploration.
 
For logic signals a logic analyzer may be what you are looking for.
Look like common USB ones are available up to 32 channels.
The software generally can do things like determine the serial baud rate and even decode some types of signals.

For a cheaper / more work option a 5v microcontroller might work.
I don't know how in-sync it would be - if there is a way to read all ports at once.
 
HP had protocol analyzers like the 4951 and similar that had several types of pods that could be used for things like RS-232, RS-449, etc. But I'm not sure that with the standard software they had the ability to deal with all of the signals like a logic analyzer. As westveld said you are probably best off with a logic analyzer that can handle the voltage ranges of the signals on those connectors. An HP 16500 or later model analyzer would handle this.
 
Do you have any idea of what kind of communication is done over the DB25? If this is serial of some sort then it most likely is compatible to standards V.24/V.28 or EIA RS-232-C Or similar. Then the pins and signal levels are defined. The actual data on the TXD and RXD pins could be just about anything. Synchronous or Async with any protocol. Then a protocol analyzer would be helpful.

On the other hand a DB25 can be anything. On a PC a DB25 could be the parallell printer port and to figure that out you would need a logic analyzer. But check so that the voltages on the port is not damaging the logic analyzer.
 
It's an old proprietary IBM thing (mid 1970s), it did communicate with a disk drive, printer, or tape drive. If I can programmatically effect any of the pins, then I'm thinking I could manage some kind of serial IO out of it (maybe only 110 baud, but that'd be fine).

The top 15-pin connector #1 is a power plug - it fits one of those 15-pin joystick connectors just fine. I don't think I need to mess with that - but the system had a huge plug and could pass 12V onto the motor of the tape system (that used a belt for QIC stuff), or I imagine whatever motor the disk drive used (same for printer).

The other two fit a DB25 style connector just fine. And as you see (below), only 10 pins on connector #3 are used.

I thought these were tied directly to the processor card - but for example, I didn't see any activity on the OpCodeE or Osc/4 pin. So maybe connected wrong, or I may need to trigger something first to activate the output from the system (there is an intermediate I/O card involved -- I thought it was just pass-thru, but maybe not).

My initial goal is to just monitor the #2 and #3 connector, to look for any kind of activity as I'm running code on the system (there are some GETB and PUTB opcodes -- I've found a partially annotated copy of the "BIOS" {executive ROS} and it uses these GETB/PUTB opcodes in the routines around where the disk drive is accessed). I just need a "broad view" probe to get my initial bearings on what/when pins get activity, then can focus down from there.

Since their harness is already the DB25 style, it'd be nice to have a probe that I could plug one of those into.

(thinking I can define a new device, like X2Y2, to be my own "communication path")


1676234666495.png
 
Won't be RS232 protocols, but I'm just looking for any activity on the pins.


Ok, going to try a HP 4951C w/ HP 18179A (I avoided the 4951A/B since they are using tape to load software, the C model is using 3.5" floppy - that I can probably find an emulator for that if it ever fails).

Also came across the EKELEC CHAMELEON 5 analyzer for under $75, will give it a try also.



Gonna pass on this $250 thing, but just wanted to mention it for reference:

www.hobbesinnovation.com

258898A TEST-i Multi-Function Data and PC Cable Tester (with DB25 Adap

TEST-i Multi-Function Data Cable Tester is a specially designed "All-In-One" cable tester that analyzes the most essential cables use today. It will test and wire-map each cable pin connection to determine open, short, cross, or miss-wired cables. Cable configurations are displayed on the LCD...
www.hobbesinnovation.com www.hobbesinnovation.com
 
These are all IBM 5110/5120 peripherals. There's a number of people working on them.
 
Why not take a different approach.

Trace the pins from the connector to where ever they go on the PCB. Some of them are probably ground, others VCC, and others probably not connected at all and can be ruled out immediately saving work.

Others might be really bleeding obvious, such as going through some kind of buffer to the CPU data bus, or into some specific chip for which you can find a datasheet.

Seeing a bunch of signals changing state is only going to reveal so much, and you're still going to have to look at their source or destination to figure out their purpose anyway, so you might as well start with that.

For now it sounds like you're trying to use too big a hammer for too small a nail.
 
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