Hi Mike
The idea of an in-circuit test of logic chips has been around for over 30 years and as wiggy said has been used in PCBA production test for as long. In fact the Genrad tester is one of the in-circuit test systems designed to do this back driving that allows a chip to be tested while loaded in a board but in isolation. Keysight still sell the i3070 series testers to this day and I expect Teradyne do too.
When I was a young fella I used a bench-top in-circuit tester for exactly what you described but I don't know if such a thing remains commercially available - mainly because you can't clip onto the legs of a ball grid array package and many fine pitch packages are going to be troublesome. If such a beast was it's price range would be more at the car end of the scale than a multi-meter...
A logic analyzer looking at the device while running would do the job but it would be dependent upon the operator to check the input and output wave-forms match the logic function of the device being tested. With my engineers hat on I can imagine a Pi Pico with a display or USB interface where you type in the part number of the chip you want to test, say 7400, it then captures the states of all the legs with the PIO and checks what it knows to be the input pins and the output pins are doing what the truth table of the selected device says it should.
The simple combinational gates such as NAND XOR NOT etc. would be relatively simple to check but the latches counters and registers could get a bit interesting as the test clip wouldn't know what the starting state would be and have to play 'catch up' to find out from the present state of the device what the next state should be. And that wouldn't always tell the whole story as, for example, a 4 bit counter used to drive a video output may be designed to get reset before it reached the maximum count of 15. The test clip would see the counter outputs get to say 9 and then go back to 0 and fail it... but its actually supposed to do that and is working fine!
Then there is the whole logic voltage level and propagation delay topics which I will not bore more on as I seem to have written an essay and not a friendly forum answer![:oops:]( "Embarassed")
So I would say is it possible to design something like this with off the shelf parts? - yes
Would it be useful? - probably yes but its not a magic bullet and like all test equipment what its telling you will need interpreting given the context
Have I seen something like it? check out https://github.com/gusmanb/logicanalyzer which appears to be a project using a Pi Pico as a logic analyzer...
Hope this helps, even if only to get you to sleep quicker![:D]( "Very Happy")
The idea of an in-circuit test of logic chips has been around for over 30 years and as wiggy said has been used in PCBA production test for as long. In fact the Genrad tester is one of the in-circuit test systems designed to do this back driving that allows a chip to be tested while loaded in a board but in isolation. Keysight still sell the i3070 series testers to this day and I expect Teradyne do too.
When I was a young fella I used a bench-top in-circuit tester for exactly what you described but I don't know if such a thing remains commercially available - mainly because you can't clip onto the legs of a ball grid array package and many fine pitch packages are going to be troublesome. If such a beast was it's price range would be more at the car end of the scale than a multi-meter...
A logic analyzer looking at the device while running would do the job but it would be dependent upon the operator to check the input and output wave-forms match the logic function of the device being tested. With my engineers hat on I can imagine a Pi Pico with a display or USB interface where you type in the part number of the chip you want to test, say 7400, it then captures the states of all the legs with the PIO and checks what it knows to be the input pins and the output pins are doing what the truth table of the selected device says it should.
The simple combinational gates such as NAND XOR NOT etc. would be relatively simple to check but the latches counters and registers could get a bit interesting as the test clip wouldn't know what the starting state would be and have to play 'catch up' to find out from the present state of the device what the next state should be. And that wouldn't always tell the whole story as, for example, a 4 bit counter used to drive a video output may be designed to get reset before it reached the maximum count of 15. The test clip would see the counter outputs get to say 9 and then go back to 0 and fail it... but its actually supposed to do that and is working fine!
Then there is the whole logic voltage level and propagation delay topics which I will not bore more on as I seem to have written an essay and not a friendly forum answer
So I would say is it possible to design something like this with off the shelf parts? - yes
Would it be useful? - probably yes but its not a magic bullet and like all test equipment what its telling you will need interpreting given the context
Have I seen something like it? check out https://github.com/gusmanb/logicanalyzer which appears to be a project using a Pi Pico as a logic analyzer...
Hope this helps, even if only to get you to sleep quicker
Statistics: Posted by SunbakedinWA — Fri Mar 15, 2024 3:29 pm