6 Nov
2011
6 Nov
'11
11:40 a.m.
But rememebr a
digital multiplexer (like the 74x151) performs a buffering
function too -- the input is 1 TTL load, the output will drive at least
10 simialr loads. This is obviously not true of the analogue
multiplexers, which are trasnmission gates. This can be important.
And it's why you can't use 4016s, etc as bidirecitonal data bus buffers.
They perform no buffering at all.
Well, yes. I like that they're just switches. Buffers have their
place, of course, but sometimes it's nice to have a little DIP IC
that'll switch off your headphone port without clicking too much.
They're fundamentally different devices.
I actually found the 4052 great for muxing a UART channel 4 ways
because you didn't have to use 2 chips; the Rx and Tx were treated
I usspect you could have fitted the logic into a PAL if you ant a 1-chip
digital solution :-). Or you could have used a pair of chips ('153 and
'139, perhaps) and multiplexed a couple of flow cotnrol singals too.
More seriously, there is no reason not to use a 4052 here. It does the
job. There is no problem with speed or fanout.
equally because they were just transmission gates. It
would only ever
be good if you were on the same PCB (or at least not going too far),
but that was what I was doing, so it was great.
They're also not particularly fast, but at least for what I was using
True, but as you rightly say, that's not always important. You'd not use
one to switch the bus lines on a multi-MHz processor. That doens't mean
they have no uses.
them for, they didn't need to be. As with
anything, it's a matter of
understanding the limitations. :-)
Of courese. I 100% agree with you. As I have said many times, it's a
mistake to think that because soemthing can't solve a particular problem,
it can't solve any problem. It's an equal mistake ot assuem that becase
(a) is better than (b) in one particualr circumstance, it must always be
better.
4000 series CMOS is an example of this. It can't solve every logic
problem, and there are families that are better in some cases. This does
not make 4000 series CMOS useless.
-tony