Texas Instruments 74LS Logic Comparators are available at Mouser Electronics. Mouser offers inventory, pricing, & datasheets for Texas Instruments . December INTEGRATED CIRCUITS. 74HC/HCT 8-bit magnitude comparator. For a complete data sheet, please also download. Part Number: 74LS, Maunfacturer: National Semiconductor, Part Family: 74, File type: PDF, Document: Datasheet – semiconductor.

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There may be better ways to do this job so keep tinkering. This would also add about 62 nS to your latch clock which right now is only 3 gate delays long and would be difficult to see on an old low bandwidth scope.

You can’t use it while the inputs are changing.

You’re depending too much on the propagation delay of the 74 and the creating a clock pulse of the minimum required width t wclk on your datasheet. A way to avoid that would be to de-glitch the circuit by adding a synchronizing flip-flop running at 16MHz just before the latching flip-flop.

If you expect to use it, datasheeet need to turn the enable off during the time when the compare inputs are in transition. This sets the D-type flip flop, which switches off the NOP generator and turns on the bus tranceivers. Just to scratch my own curious itch, what does the connect to? This datxsheet all fine. I’ve never had to use one. My calculations say yes, with lots of time to spare, but I’d like others’ opinions.


I got lost reading that. Here’s the pieces relevant to Power on Jump: I’m currently designing the power-on-jump circuit for my processor board.

This might cause a false trigger if your address trap was at B. Glitchy output shouldn’t be a problem — it needs to be inverted for the D-type flip flop’s clock anyway, so I’m using a 74LS14 inverter, which has Schmitt inputs and should clean up vatasheet signal into a nice, sharp positive-going square wave.

I don’t do well with word descriptions of circuits–can you draw a schematic? Hi No it won’t. It is a glitchy signal. Any decoder, like the will create big nasty full swing glitches that can only be removed with the proper clocked gating or latching.

It might work, but I don’t like it much.

74LS Datasheet, PDF – Alldatasheet

It’s an 8-bit comparator, but it’s cheaper than the 74LS85 and has an enable input. It’s comparing the high four address bits to a 4-position DIP switch. I’m not talking about little tiny noise spikes. When the system comes up from a reset, a 74LS with its inputs all tied to ground is connected to the data lines of the CPU and the data bus tranceivers are switched off — this feeds the CPU NOPs until the address equals what’s set on the DIP switch.


74LS688 PDIP20

It may even make it worse. You could then use it as a clock. As the address lines transition and settle out, they might very well set up a glitch that agrees with the test condition, well before you intended.

Glitchy output shouldn’t be a problem — glitch, I see how you got your nickname. I’m not that good with circuit design, but is it possible a monostable multivibrator 74lls688 would do the job? Hi I doubt you’ll be able to run the output of the directly to a clock. For example, going from 9 to A might give a false compare of B for a few nanoseconds. In other words, what function does it serve? Note dafasheet this would take away 62 nS from the access time of the first instruction fetch after the proper address compare, but it should be OK if you are using newer memory devices.