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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Glitchy output shouldn’t be a problem — glitch, I see how you got your nickname.

My calculations say yes, with lots of time to spare, but I’d like others’ opinions. I don’t do well with word descriptions of circuits–can you draw a schematic? I’m not datasheett about little tiny noise spikes.

74LS688 8-bit Magnitude Comparator

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

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.


74LS688 Datasheet PDF

In other words, what function does it serve? Hi I doubt you’ll be datxsheet to run the output of the directly to a clock. 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.

It’s comparing the high four address bits to a 4-position DIP switch. If you expect to use it, you need to turn the enable off during the time when the compare inputs are in transition.

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 the signal into a nice, sharp positive-going square wave. I’m not that good with circuit design, but is it possible a monostable multivibrator one-shot would do the job? It may even make it worse.

Propagation delay question [Archive] – Vintage Computer Forum

Here’s the pieces relevant to Power on Jump: It is a glitchy signal. Just to scratch my own curious itch, what does the connect to? 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. This is all dataasheet.


It’s an 8-bit comparator, but it’s satasheet than the 74LS85 and has an enable input. 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. There may be better ways to do this job so keep tinkering. I got lost reading that. Hi No it won’t.

74LS Datasheet PDF –

It might work, but I don’t like it much. You could then use it as a clock.

Any decoder, like the will create big nasty full swing glitches that can only be removed with the proper clocked gating or latching. This might cause datsaheet false trigger if your address trap was at B. This sets the D-type flip flop, which switches off the NOP generator and turns on the bus tranceivers. I’m currently designing the power-on-jump circuit for my processor board.

I’ve never had to use one.

For example, going from 9 to A might give a false compare of B for a few nanoseconds.