Fun With A Logic Analyzer
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Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Fun With A Logic Analyzer
I bought a mid-'80s HP 1651B logic analyzer really cheap on eBay. It's the same vintage as my ECM, so that's fine.
I built an ECM test box that simulates various inputs and has status LEDs so I can monitor the outputs. It's about 80% complete right now. It's interesting to see the IAC calibrate after the ignition is turned off (red/green LEDs). I also have an ALDL connector that I can hook up to my laptop to monitor what's happening.
I bought a connector that plugs into the edge connector on the ECM PC board. That's really convenient because it's a HUGE pain to connect the logic analyzer probes to the microcontroller, especially when it's coated with conformal coating.
All hooked up and running. I'm having a problem with the data display, though. Something is not set up correctly. The program code addresses are OK but the data is garbage. I think maybe it's grabbing the data at the wrong time in the clock cycle.
[ EDIT ] It turned out that I had the wrong EPROM in the ECM. It was an APYP that was in there when I bought the ECM. I took off the label to reprogram it (which in retrospect was a bad idea, given what original EPROMs are going for). Everything's peachy now. [ /EDIT ]
Here it is running off my antique power supply that I built back in the '70s from an article in Popular Electronics magazine:
The cool thing about a logic analyzer is that you can set it up to start recording when it hits a certain address or a variable changes in memory. You can trace the path through the code in real time and see exactly what the ECM is doing and when. Fun stuff.
I built an ECM test box that simulates various inputs and has status LEDs so I can monitor the outputs. It's about 80% complete right now. It's interesting to see the IAC calibrate after the ignition is turned off (red/green LEDs). I also have an ALDL connector that I can hook up to my laptop to monitor what's happening.
I bought a connector that plugs into the edge connector on the ECM PC board. That's really convenient because it's a HUGE pain to connect the logic analyzer probes to the microcontroller, especially when it's coated with conformal coating.
All hooked up and running. I'm having a problem with the data display, though. Something is not set up correctly. The program code addresses are OK but the data is garbage. I think maybe it's grabbing the data at the wrong time in the clock cycle.
[ EDIT ] It turned out that I had the wrong EPROM in the ECM. It was an APYP that was in there when I bought the ECM. I took off the label to reprogram it (which in retrospect was a bad idea, given what original EPROMs are going for). Everything's peachy now. [ /EDIT ]
Here it is running off my antique power supply that I built back in the '70s from an article in Popular Electronics magazine:
The cool thing about a logic analyzer is that you can set it up to start recording when it hits a certain address or a variable changes in memory. You can trace the path through the code in real time and see exactly what the ECM is doing and when. Fun stuff.
Last edited by Cliff Harris; Jan 7, 2014 at 11:27 PM. Reason: Added note.
Thread Starter
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
I used one like this back around 1995. It was too expensive to own so my company rented it. I saved the company a lot of money and trouble when I found a problem using one of these that we had been receiving complaints about for over a year. I never would have found the problem without it.
Safety Car
Joined: Nov 2009
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From: Adelaide South Australia
Safety Car
Joined: Nov 2009
Posts: 3,973
Likes: 341
From: Adelaide South Australia
