1 Feb
2025
1 Feb
'25
7:10 p.m.
On Feb 1, 2025, at 8:37 AM, Frank Leonhardt via cctalk
<cctalk(a)classiccmp.org> wrote:
On 01/02/2025 02:31, roger arrick via cctalk wrote:
So did early logic ICs. TTL happens to be very well known because it was far more
successful than others, but it was preceded by DTL (6 volts) and RTL (3.6 volts). Also,
in the days of TTL, you might also find high end systems with ECL in them (-3 volts??? I
forgot).
And yes, of course in discrete transistor computers the voltages would be all over the
map. 6 volts in the CDC 6000 mainframes, who knows what else in other machines of that
era.
paul
In 1977, at age 16, I went to work for Noakes
Data Communications in Irving Texas.
We built an 8080 industrial computer, made modems, and repaired lots of comm gear.
RS232 was what we lived and breathed. And back then almost all the control signals were
actually used, not just jumpered or ignored.
I remember thinking at the time that the bipolar signal levels were such a waste of time
for office and personal computers. They should have just gone to a TTL version for
everything local like printers, and modems, and keyboards and terminals. Back then we had
to use 1488 and 1489 level converters with +/-12v power supplies. Such a costly hassle.
Of course, many years later we got MAX232 with 4 .1uf caps and 5v which solved the cost
problem.
...
I certainly agree TTL would have made sense for microprocessors but earlier computers ran
at much higher voltages, and lots of them :-)