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.

Author: Volkis Mojas
Country: Great Britain
Language: English (Spanish)
Genre: Video
Published (Last): 13 October 2017
Pages: 477
PDF File Size: 4.57 Mb
ePub File Size: 11.66 Mb
ISBN: 312-9-97815-488-6
Downloads: 71744
Price: Free* [*Free Regsitration Required]
Uploader: Goramar

You can’t use it while the inputs are changing. Here’s the pieces relevant to Power on Jump: Hi No it won’t.

(Datasheet) 74LS pdf – SN74LS (1-page)

It may even make it worse. This might cause a false trigger if your address trap was at B. If you expect to use it, you need to turn the enable off during the time when the compare inputs are in transition. I’ve never had to use one. A way to 74l6s88 that would be to de-glitch the circuit by adding a synchronizing flip-flop running at 16MHz just before the latching flip-flop.

Datasneet example, going from 9 to A might give a false compare of B for a few nanoseconds. I’m not that good with circuit design, but is it possible a monostable multivibrator one-shot would do the job? I’m not talking about little tiny noise spikes. It might work, but I don’t like it much. Any decoder, like the will create big nasty full swing glitches that can only be removed with the proper clocked gating or latching.


I got lost reading that. 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 datasheet OK if you are using newer memory devices.

This sets the D-type flip flop, which switches off the NOP generator and turns on the bus tranceivers. It’s comparing the high four address bits to a 4-position DIP switch.

Propagation delay question [Archive] – Vintage Computer Forum

My calculations say yes, with lots of time to spare, but I’d like others’ opinions. In other words, what function does it serve?

It’s an 8-bit comparator, but it’s cheaper than the 74LS85 and has an enable input. There may be better ways 74l688 do this job so keep tinkering. You could then use it as a clock. This is all fine.

Comparator 74LS688 DIP20

Hi I doubt you’ll be able to run the output of the directly to a clock. 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.


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. 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

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.

It is a glitchy signal. This would also add about 62 nS to your latch clock which right now is only 3 datasehet delays long and would be difficult to see on an old low bandwidth scope. Glitchy output shouldn’t be a problem — glitch, I see how you got your nickname.

I don’t do well with word descriptions of circuits–can you draw a schematic? Just to scratch my own curious itch, what does the connect to?

Back to top