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.

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 datqsheet — this feeds the CPU NOPs until the address equals what’s set on the DIP switch. It’s comparing the high four address bits to a 4-position DIP switch.

I don’t do well with word descriptions of circuits–can you draw a schematic? Datashret could then use it as a clock. It is a glitchy signal. I’m not talking about little tiny noise spikes. 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.

I’m currently designing the power-on-jump circuit for my processor board. It’s an 8-bit comparator, but it’s cheaper than the 74LS85 and has an enable input.


74LS688 PDIP20

If you expect to use it, you need to turn the enable off during the time when the compare inputs are in transition. 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.

This would also add about 62 nS to your latch clock datasheeh right now is only 3 74,s688 delays long and would be difficult to see on an old low bandwidth scope.

It may even make it worse. Any decoder, like the will create big nasty full swing glitches that can only be removed with the proper clocked gating or latching. For example, going from 9 to A might give a false compare of B for datawheet few nanoseconds. You can’t use it while the inputs are changing. Here’s the pieces relevant to Power on Jump: This is all fine. In other words, what function does it serve? It might work, but I don’t like it much. My calculations say yes, with lots of time to spare, but I’d like others’ opinions.

Comparator 74LS688 DIP20

Hi I doubt you’ll be able to run the output of the directly to a clock. 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 ddatasheet the signal into a nice, sharp positive-going square wave.


I got lost reading that. 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. Note that 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. I’m not that good with circuit design, but is it possible a monostable multivibrator one-shot would do the job?

This might cause a false trigger if your address trap was at B.

74LS datasheet,datasheets manu Page:5====[未知厂家] pdf datenblatt – –

Just to scratch my own curious itch, what does the connect to? I’ve never had to use one. Glitchy output shouldn’t be a problem — glitch, I see how you got your nickname.

Hi No it won’t. This sets the D-type flip flop, which switches datashret the NOP generator and turns on the bus tranceivers.

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