15 Jan
2008
15 Jan
'08
10:56 p.m.
OK, I'm building the bit-serial ALU for my 2N2/256 project. Though
it sounds exceedingly elementary, one design variable I haven't been
able to figure out is what supply voltage I should use.
Does anybody know why the 7400-series TTL used +5V for Vcc? I've
looked at the equivalent circuits for TTL and LSTTL. Maybe I'm
missing something, but it's not immediately obvious to me why such
circuits couldn't operate on, say, 4.5V or 6V. I understand the need
for good regulation to maintain noise margin, but why in 1964 did
Texas Instruments chose 5V in particular for TTL? Was it just an
arbitrary choice, or is there a deeper issue?
-Bobby