SubscribeDifferences between 7476 Dual JK Flip-Flop Chips.?
Our class is working on a lab that uses chain of a Grayhill 12-button keypad, an 74147 encoder, a 7404 inverter, two 7476 dual JK flip-flops (to store and clear the number from the keypad), a 7447 decoder, and a Common Anode 7-segment display.
Does anybody have any experience with different 7476 dual JK flip-flops working in some circuits and not in others? Example: DM7476 National Semiconductor and 7476 with no name?
Thanks for your time.
School lab IC's are notorious for being damaged, so it wouldn't be the first time...
However, you may have a circuit timing problem that the change in IC's demonstrates. If you have a race condition or metastability, a different IC, even from the same vendor, can fail while another does not. You could have some F/F's (flip-flops) that work fine, even if the setup and hold times are violated, while the others do not and require the timing specs to be met. Remember the data sheets are only for guaranteed operation; the parts may or may not still operate when the specs are not met.
A look at the TI data sheet (link below) shows a very interesting fact. The 7476 is a POSITIVE-edge F/F; the 74LS76A is a NEGATIVE-edge F/F! Could your no name version be a 76A? Or the National part? (No wonder this wasn't a very popular part!)
If I were trying to make sure this worked, with the existing parts list, I'd probably use the 7404 to invert the four '147 outputs (just for delay purposes). I'd use the Common from the keyboard to strobe the F/F clears and use the inverted '147 outputs for the presets. Then I'd use the F/F Q-bar outputs to go to the 7447. The Common should go inactive (High) well before the inverted '147 outputs and clear all the F/F's (Q-bar will be High if the inverted '147 output, i.e. preset, is High). If the inverted '147 outputs are Low, they will preset the F/F's, so Q-bar will be Low on those. The result will be correct out of the 7447 and the display. This eliminates any clock timing issues and the extra delay of the inverters should make the preset pulse width long enough to ensure proper F/F operation (assuming no switch bounce problems and that the keypress output timing is identical to the Common output timing). And this will work with 7476 or 74LS76A parts, since the clock is not used.
Good Luck!
Flip Flop Circuit
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