I just wonder why a measure 3.36V (instead of the 5V - TTL) on the data pins of my parallel port (I put my voltmeter directly between the data pin #0, set to logical 1, and the ground)?
I'm sure I forgot something but I appreciate if someone can help me. Thanks! Fred
3.36 volts is a legal, and fairly ordinary, TTL high level. True TTL drivers never did pull all the way up to +5.
John
Perhaps so, but 3.36 is still a legal TTL high. Classic TTL parts were usually specified for a min Voh in the 2.5-2.7 sort of range, and typs around 3.4.
Slide rule? How dated! I use an HP-35.
John
My laptop gives almost exactly 3.3 V. I would bet that it's 5 volt tolerant
3.3 volt CMOS.Jonathan
John
Hello John,
This must be a pretty old system if it has TTL chips in there instead of CMOS. Probably right after the abacus and the slide rule calculator (which I am still using...).
Regards, Joerg
Hello John,
Ok, I also use an HP-11C. But when I have to calculate RC, resonant circuits, filters or stuff like that I sometimes crack out the old slide rule calculator. This speeds up the calcs when I want to stay within a range of already released part values or within a standard series. It does raise eye brows at times. At one client they reminded me that they do have Edison electric light.
Regards, Joerg
voltage
Yes, but 3.3 V CMOS will produce legal TTL levels.
Jonathan
It is probably the design of your motherboard. Probably a 3.3v setup.
Maybe you have a 'retro' chipset that emulates TTL levels ? There isn't a 'toob' in there as well is there ? ;-)
Graham
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Graham
As John has implied, the spec actually stated that it was to be TTL voltage levels on those pins.
Ken
Yes indeed. I think we've all satisfactorily surrounded the answer from all directions and can go home happy. :-)
Cheers.
Ken
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