Hi All,
In my quest to get my Game Plan MPU working, I have a generic question about logic gates. When the output of a gate is determined to be high, should the voltage be close or equal to Vcc, or is it somehow equal or proportional to the input? For example, if one of the inputs of a 74LS32 OR gate is 3.0v, would the output also be 3.0v? Or, should it be closer to 5.0v? Would the same apply to an inverter? Assume Vcc is 5.0v and ground is good.
Thanks,
Tom
Take a look at your data sheets. They should say what input level is considered high and low, and what range they'll drive the output at (high and low) too.
Generally though if you nave a buffer chip running at 5v, and you put 3 in, you'd expect 5 out. That's why they're "logic" chips and lot analog.
For (LS)TTL chips, usually anything over 3V or so is considered to be "high", and under 0.8V is "low". If you see a voltage between 0.8 and 3 volts, there might be a bad chip or short somewhere.
But note that if you measure rapidly changing signal with a multimeter, it will only show the average voltage.
According to the data sheets, typical high output is 3.4v. That is with a 2.0v input, the minimum for high input. I can't find any information that would indicate, one way or the other, if the output voltage changes in relation to input voltage.
Quoted from Rapid_Roy:I can't find any information that would indicate, one way or the other, if the output voltage changes in relation to input voltage
again, for a logic chip like an or gate, they're logic. binary. it only cares if the input is high or low.
Quoted from Rapid_Roy:Yes, I know that. I am trying find out why the reset pin of the cpu is not getting the full 5.0v.
What chip in particular are you looking at?
Edit...oops, didn't notice you already mentioned it.
Quoted from Rapid_Roy:Yes, I know that. I am trying find out why the reset pin of the cpu is not getting the full 5.0v.
Looking at the chip, with a 5V supply and a 1mA load - the output should be between 2.7 and 4.3V
pasted_image (resized).pngThe reset signal you're looking at on your GamePlan MPU board is transistor driven, not logic chip driven.
The Z80 CPU it goes into is TTL based. Z80 specs say logic low is 0.8V or less, logic high is 2.2V or higher. 0.9V to 2.1V is indeterminate.
For everyone else:
https://pinside.com/pinball/forum/topic/game-plan-mpu-2-won-t-boot
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