Supply voltage for 2N2/256-BSCP

Robert Nansel bnansel at
Tue Jan 15 16:56:14 CST 2008

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?


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