Help needed with logic probe pulses

colonelsnow

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I am trying to learn to use a logic probe to trouble shoot boards. Attached are the "instructions" for my probe. I am having a hard time understanding when the correct state for a pin would be high with "no pulse activity" vs high with "negative single pulses"? For example should the normal state of the reset pin on a 6502 be high with "no pulse activity" or "negative single pulses"?
 

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I am trying to learn to use a logic probe to trouble shoot boards. Attached are the "instructions" for my probe. I am having a hard time understanding when the correct state for a pin would be high with "no pulse activity" vs high with "negative single pulses"? For example should the normal state of the reset pin on a 6502 be high with "no pulse activity" or "negative single pulses"?

Reset pins are usually 'no pulse activity'. Your probe is certainly better than mine - I just get hi/lo/flashing :)
 
Watch these. Adam is a member here and explains things remarkably well!



 
I am trying to learn to use a logic probe to trouble shoot boards. Attached are the "instructions" for my probe. I am having a hard time understanding when the correct state for a pin would be high with "no pulse activity" vs high with "negative single pulses"? For example should the normal state of the reset pin on a 6502 be high with "no pulse activity" or "negative single pulses"?

Like Jam Burglar was saying, you're going to have to read a lot to kind of understand how they work. You don't really need to know how the probe works, you need to know how the CIRCUITS work. After awhile you'll get familiar with some of the chips and their function, like for instance a lot of boards will have buffer chips, and rom chips, and ram chips... they'll have different numbers, but work the same. So on their address lines, you'll see them pulsing away quickly... but there will also be a line that enables the chip, or reverses it's direction, or whatever that will either stay high, or low, or pulse depending on the schematic and what circuit it's used in.

Watch those videos he put up and it'll give you a good basic understanding, then you can work through a board chip by chip and learn a lot. On a 6502, they typically start low when the board is first turned on, then within a second or so will go high and stay high. if they go low, since that line is 'active low', the low pulse resets the chip. Depending on the game, you see different behavior... for instance, in an Asteroids that line will reset a couple times a second if it's in watchdog mode... but in a Battlezone, I've seen that line only reset each 10 seconds if it's in watchdog mode. A normally working board in either game should never go low after it goes high.
 
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