> On Feb 1, 2025, at 8:37 AM, Frank Leonhardt via cctalk
> <cctalk@classiccmp.org> wrote:
>
> On 01/02/2025 02:31, roger arrick via cctalk wrote:
>> 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 :-)
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
