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Is it advisable to mix logic families?

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vsmGuy

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Mixing logic families

Guys,

Is it advisable to interface LS family digital logic parts with a uC like AT89C52 or PIC, or should I use HC parts instead ?

For example, would it be a good idea to connect a 74LS74 to the above mentioned uC pins or would it be better to connect a 74HC74 ?

An anecdotes and ideas/suggestions ?
 

Mixing logic families

there is no problem at all using LS

and in both cases some times u need to use buffer ICs like 74245
again 74LS245 mostly used
 

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    vsmGuy

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Mixing logic families

The ATMEL 89 series and PIC seem to have TTL compatible IO. Hence, LS should not be a problem.

I was sorry I did not mention this, because I had a mind block with the clock freq.

What I was querying about was whether anyone had speed sync issues.

LS logic hit the max at ~25Mhz whereas HC at ~65Mhz, unless I am mistaken.
 

Mixing logic families

it may create problem if we use high freq signal but we cant use even 20 MHz in case of 8951 8952. i think you can now easily get my point
 

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    vsmGuy

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Mixing logic families

Yes, indeed. You have a very important point there.

For such slow speed uC, we don't need high speed glue.

Do we ?

I don't think so.

Unless we are making hardware to slow down a faster device to interface with the slower uC.
 

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