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'[OT] logic levels (was Re: More RS232 to PIC quest'
|Wagner Lipnharski wrote:
>When using logic chips that use VCC=5V we can say "that logic is
>TTL...". What is the logic's name when using CMOS at 8V or the low
>voltage chips at 3.3V? The TTL (Transistor Transistor Logic) is widely
>used to means zero and +5V logic, but... it gets confused, isn't?
Actually, the term 'TTL level' is a VERY useful term these days. I use low
voltage devices that are 'TTL' compatible - this means they will accept a
TTL high without complaining, they will output a HI level that other TTL
compatible chips will read without error, and the switching threshold is
somewhere near the middle of the TTL 'no-mans-land' of 0.8V to 2.0V. In
fact, TTL compatible levels is one of the criterea I look for when choosing
devices - most everything I do eventually has to talk to exiting equipment.
Kinda neat that 30 year old logic level definitions are still useable!
Dwayne Reid <planet.eon.net> dwayner
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(403) 489-3199 voice (403) 487-6397 fax
Celebrating 15 years of Engineering Innovation (1984 - 1999)
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Dwayne Reid wrote:
> fact, TTL compatible levels is one of the criterea I look for when choosing
> devices - most everything I do eventually has to talk to exiting equipment.
A very good idea as I was recently bitten by a 'gotcha' which would not
have happened had I not got complacent in my old age! I've gotten so
used to lowering my current consumption that I've slowly increased bias
resistors because, hey 5V parts output 5V right? Well, pretty close
certainly no less than 4V, right?
Eh, no - not right. Particularily where CPLD's are concerned. Most state
'TTL' comptable and use every inch of the TTL spec.
At 11:37 04/08/99 -0600, Dwayne Reid wrote:
>most everything I do eventually has to talk to exiting equipment.
exiting job you have! :)
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