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7402 Pinout Difference

AnalogKid

Well-Known Member
Most Helpful Member
Both images are correct.

The image on the left is for a CMOS CD4001. This is NOT directly equivalent to a bipolar SN7402 in the right image, either electrically (voltages and currents) or physically (pinout). Note that the left image power pin is Vdd (the correct designation for a CMOS part) as opposed to the right image of a Bipolar TTL part with a power pin labeled Vcc. This is because a bipolar transistor has a collector (c) while a CMOS transistor has a drain (d).

cc stands for common collector, a type of amplifier circuit. When FET logic came about, they changed the last letter to d for drain. Rather than use the technically correct Vcd (Voltage, common-drain), they went with dd for consistency and error reduction

ak
 

jack0987

Member
Thanks for the response.

I am using the TTL one (an MC74HC02) on the right.

Is it good practice to to ground all unsed inputs?
 
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
Thanks for the response.

I am using the TTL one (an MC74HC02) on the right.

Is it good practice to to ground all unsed inputs?
Probably, a lot depends on the circuit configuration in the chips (might be better both high, might already be pulled high or low internally?), and if you're wanting minimum power consumption - it's more of an issue in CMOS, where inputs can drift and put the gate in an analogue state, greatly increasing consumption.
 

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