74HCT688 8-bit comparator (PART 1)

After two nights of struggle, I finally got that IC to output something that was looking nice to me. Once again there is no secrets just read the fucking datasheet (RTFDS). This time i had read the datasheet to check about the pinout and the voltage. I had just missed reading the “function table”. I was wrongly assuming that the G or E pin was in the need to be high in order to accept an input. The other thing i got wrong was the fact that i tought that the 74HCT688 will output high on “P=Q” being true, no, it’s just the inverse … when condition is false it output high and when it’s true output low.

74HCT688 function table

So what’s next ? First I want to finish the breadboard layout like I wanted it to be. That means : 1 eight position dip-switch, 1 74HCT688 and a led My experimentation will be to compare 4 high bits with 4 low bits of the dip-swith and to turn on the led on when high and low bits match. Currently, this is my breadboard.

Part one of 74HCT688 experimentation

As you can see I now need to wire the dip-switch to the IC and get somekind of inverter or XOR gate to turn on the led when result is low.

See ya, Lint

Comments are closed.