# Identifying 74xx series logic IC

There are Logic IC testers which can identify the type of IC, like 7400, 7404, or 74138, etc. How can I implement the process in my testing code?

Apply logic values to the all the inputs of the IC you are testing and for each set of input values, read the outputs of the IC. Compare the results with a truth table for the IC.

jremington:

Thank you for fast responding.

How do you know if the chip is 14 dip or 20 pin to apply Vcc and Vss, or if pin 1 is for logic input or clock input, etc?

My question is how to identify a logic IC out of hundreds.

Edit: I changed the title.

nadana: How do you know if the chip is 14 dip or 20 pin to apply Vcc and Vss, or if pin 1 is for logic input or clock input, etc?

Yes, that right there is the gist of the problem.

You may find that with careful probing of pins and looking at current consumption and pin impedance, using current limited supplies, you might be able to guess which pins are the power supply. But I'm sure the circuitry would not be trivial.

Once you figure out the power supply, I suppose you could then measure voltages of all pins and guess which are outputs, and which are inputs. Figuring out the difference between a tri-state output and an input would be a little more difficult, but by probing and measuring current you could probably tell the difference because I would think an input will have a lower impedance.

Now, with the power, input, and output pins determined, look up all of the chips that match that profile. Then start running the truth tables trying different input combinations and watching outputs. Repeat for each possible chip until a match is made.

All in all, a rather daunting proposition. It's probably a whole lot easier to just read the number printed on the chip. ;)

ShapeShifter: Thank you. That is the idea from where I started. But eventually I came to this question,"What if the chip under test is a bad chip?"

ShapeShifter: ... All in all, a rather daunting proposition. It's probably a whole lot easier to just read the number printed on the chip. ;)

This question is just for curiosity because there are some testers on the market which can identify the chip.

Regards,

They are cheap. Just buy new ones with the number printed on them.

...R

Robin2:
They are cheap. Just buy new ones with the number printed on them.

…R

I have two ic testers and have no intention to build one. I know all the numbers of ic before testing.

The purpose of this post: I’d like to know what algorithm they used to identify the chip, like this one: http://goo.gl/8NjAZY

Regards,

Robin2: They are cheap. Just buy new ones with the number printed on them.

...R

And if there's no number on them, how does he know that they are 74XXX series IC's? They could be anything.

nadana: The purpose of this post: I'd like to know what algorithm they used to identify the chip, like this one: http://goo.gl/8NjAZY

I can't find any information on that module, other than the vague description (which is repeated identically on all pages mentioning the units.) clicking on the more details links on any if these pages takes you to a manufacturer's page that does not have that product. I'd like to see a manual on it to get more details.

From the vague comments, it's not clear whether the module can identify a random chip, or if it just tests a chip once you tell it which one it is. If it really can detect the chip type, I'm surprised that it can be done reliably and safely with such a low cost device.