Circuit debugging question. Re an 8-bit comparator

[owhite]

I am trying to make a circuit similar to the one I described here:

http://cnczone.com/forums/showthread.php?t=5366

except this binary counter will have 8-bit resolution. I have some circuit simulation software and when I hook my 74LS682 in the following way I cant seem to get it to register that word it is comparing has changed, that is, it goes from 00000000 to 00000001 when I depress the button.

Any suggestions?

Owen

[pminmo]

As depicted, when you press the button, they will be equal. There are unequal in the undepressed state. As show pin 19 will be false (hi), when you push the button and make equal it will go true (low).

Phil

[owhite]

I guess i could put the question this way: why does my simulator give the same voltages for these two different circuits?

o

[Al_The_Man]

Owen, Is it because it is a 3state device? I do not have a spec sheet for this, do you have a link for it? I saw one application where p0 was designated AEN (address enable). I found the app sheet, what happens in the simulator if you place a pull-up resistor on the metered pin?
Al

[owhite]

Spec sheet.

http://www.nilno.com/laser_dir/pdf/74ls684.pdf

[pminmo]

I don't think it should. No it's not a tristateable.

Phil

[owhite]

grumble.

owen

[DR-Motion]

Owen,

Just an observation... but I don't see a Vcc and GND connection for the 'LS682...just for the logic inputs.

Gary

edit... or maybe your simulator does it for you?

[owhite]

yeah the simulator assumes those get hooked up and doesnt display 'em.


o.

[tachus42]

Works for me using B2 Spice must be something not quite right with your simulation setup or part model.

[owhite]

tachus,

what was designation of chip did you use? 74LS5684 or something else?

and thanks much for taking the time to try it out.

owen

[tachus42]

It was the ls682.