What is the "complement" to the 74LS154?

[JerryH]

I'd like to construct a multiplexed-demultiplexed control circuit. I've located specs easily enough on the 74LS154 (4-to-16 line decoder), but I can't seem to find what amounts to a 16-to-4 line encoder. I know about using a pair of 8-to-3's to get the equivalent function, but I'd like to know if a 16-to-4 exists.

Thank you for any help you can provide.

[sghioto]

JerryH

I don't think there is one. The closest single chip I know of is the 74147, a 10 to 4 line decimal encoder.

Steve G.

[JerryH]

Thank you for the response.

After a little more digging, it seems that the '154 is primarily for memory addressing, so it's unlike the reverse of it was ever really needed.

Oh well.

[Gorgon]

You could make the 16 to 4 decoder yourself with a eprom(or flash) with 16 address lines, like the 27(8/9)xx512. Program it for the different values and get whatever combination outputs you want. I have never heard about a 16 to 4 bit decoder or priority encoder type chip.

TOK

[haklesup]

Check out the 74LS138 1 of 8 Decoder/Demux

The 74AS250 is close but I think not quite

And yes, you can make these out of all 74xx00 NAND or just about any kind of programmable logic family with a sufficient number of I/O pins.

[Dean Huster]

Closest thing used to be the 74150, but it was not available in an "LS" version as I recall. We always paired 74154 with a 74150 for a MUX/DEMUX circuit. The '150 is a 1-of-16 multiplexer. You can easily cascade two 1-of-8 MUXs and do it in LS, but you'll need an additional inverter for the enable pin of the second MUX.