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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74LS688 Datasheet PDF

If you expect to use it, you need to turn the enable off during the time when the compare inputs are in transition. I’m not talking about little tiny noise spikes. This sets the D-type flip flop, which switches off the NOP generator and turns on the bus tranceivers. You can’t use it while the inputs are changing.

Just to scratch my dataeheet curious itch, what does the connect to? I’m not that good with circuit design, but is it possible a monostable multivibrator one-shot would do the job?

I’ve never had to use one. Any decoder, like the will create big nasty full swing glitches that can only be removed with the proper clocked gating or latching.

74LS688 Datasheet

I don’t do well with word descriptions of circuits–can you draw a schematic? Hi No it won’t. My calculations say yes, with lots of time to spare, but I’d like others’ opinions. It may even make it worse. In other words, what function does it serve?


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

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. eatasheet

Glitchy output shouldn’t be a problem — glitch, I see how you got your nickname. 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 xatasheet and should clean up the signal into a nice, sharp positive-going square wave.

This is all fine.

I got lost ratasheet that. There may be better ways to do this job so keep tinkering. When the system comes up from a reset, a 74ld688 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.

It’s an 8-bit comparator, but it’s cheaper than the 74LS85 and has an enable input. Note that this datwsheet 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.


Here’s the pieces relevant to Power on Jump: It might work, but I don’t like it much.

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. Hi I doubt you’ll be able to run the output of the directly to a clock. 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. It’s comparing the high four address bits to a 4-position DIP switch. I’m currently designing the power-on-jump circuit for my processor board.

It is a glitchy signal. You’re depending too much on the propagation delay of the 74 and the creating a clock pulse of 74ps688 minimum required width t wclk on your datasheet. For example, going from 9 to A might give a false compare of B for a few nanoseconds.