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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I got lost reading that. 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 might work, but I don’t like it much. This sets the D-type flip flop, which switches off the NOP generator and turns on the bus tranceivers. My calculations say yes, with lots of time to spare, but I’d like others’ opinions.

It’s comparing the high four address bits to a 4-position DIP switch. 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 74ld688 you are using newer memory devices.

There may be better datasheett to do this job so keep tinkering. This is all fine. In other words, what function does it serve? If you expect to use it, you need to turn the enable off during the time when the compare inputs are in transition.


When the system comes up from a reset, a 74LS with its inputs all tied to ground is connected to the data dahasheet 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.

74LS 데이터시트(PDF) – TI store

Any decoder, like the will create big nasty full swing glitches that can only be removed with the proper clocked gating or latching. 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. 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.

It’s an 8-bit comparator, but it’s cheaper than the 74LS85 and has an enable input. I’ve never had to use one. Glitchy output shouldn’t be a problem — glitch, I see how you got your nickname.

74LS datasheet & applicatoin notes – Datasheet Archive

It is a glitchy signal. I don’t do well with word descriptions of circuits–can you draw a schematic? I’m not talking about little tiny noise spikes. Just to scratch my own curious itch, what does the connect to?


It may even make it worse. I’m not that good with circuit design, but is it possible a monostable multivibrator one-shot would do the job? Here’s the pieces relevant to Power on Jump: This might cause a false trigger if your address trap was at B.

Hi No it won’t.

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.

Comparator 74LS688 DIP20

Glitchy output shouldn’t be a datadheet — 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. You can’t use it while the inputs are changing.

I’m currently designing the power-on-jump circuit for my processor board. 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.

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