Mixing 4000 and 7400 Series

Your 4000 series slows down at 5V and your LS blows up over 5V. Is that acceptable?

Mixing logic families is mostly OK but things like reset/preset are often logic low for TTL and high for CMOS along with limited drive from CMOS. I'm sure most everyone has done it at some time. I know I have.

GG

Your 4000 series slows down at 5V and your LS blows up over 5V. Is that acceptable?

Mixing logic families is mostly OK but things like reset/preset are often logic low for TTL and high for CMOS along with limited drive from CMOS. I'm sure most everyone has done it at some time. I know I have.

GG

Thanks,

The circuit is spread across multiple PCBs with this CMOS/TTL problem on it's own board. So in theory I should (and can) increase the supply voltage on the CMOS bits of the circuit and keep the TTL parts still at 5V? That should reduce the operating speed difference somewhat correct?

There's no reset type pins it's just purely data that will be sent between the two that makes thing's slightly simpler.

Cheers,

Michael

A 4000 series CMOS gate will drive ONE 74LS series standard input adequately, provided (1) the CMOS has 5V power supply and (2) the two chips are at the same temperature. CMOS sinks inadequate current when it's hot for a 74LS input when that LSTTL chip is cold.

And, an output from a 74LS gate will drive a CMOS gate adequately if you add a pullup resistor (for highest performance, 4k ohms to +5V).