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Parallel port question?

F

Fred

Jan 1, 1970
0
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
 
J

John Larkin

Jan 1, 1970
0
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
 
J

Joerg

Jan 1, 1970
0
Hello John,
3.36 volts is a legal, and fairly ordinary, TTL high level. True TTL
drivers never did pull all the way up to +5.

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
 
J

John Larkin

Jan 1, 1970
0
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...).

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
 
J

Jonathan Westhues

Jan 1, 1970
0
John Larkin said:
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.

My laptop gives almost exactly 3.3 V. I would bet that it's 5 volt tolerant
3.3 volt CMOS.

Jonathan
http://cq.cx/
 
J

Joerg

Jan 1, 1970
0
Hello John,
Slide rule? How dated! I use an HP-35.

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
 
K

Ken Taylor

Jan 1, 1970
0
Jonathan Westhues said:
message


My laptop gives almost exactly 3.3 V. I would bet that it's 5 volt
tolerant
3.3 volt CMOS.

Jonathan
http://cq.cx/
As John has implied, the spec actually stated that it was to be TTL voltage
levels on those pins.

Ken
 
J

Jonathan Westhues

Jan 1, 1970
0
Ken Taylor said:
As John has implied, the spec actually stated that it was to be TTL voltage
levels on those pins.

Yes, but 3.3 V CMOS will produce legal TTL levels.

Jonathan
http://cq.cx/
 
S

Si Ballenger

Jan 1, 1970
0
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

It is probably the design of your motherboard. Probably a 3.3v
setup.
 
K

Ken Taylor

Jan 1, 1970
0
Jonathan Westhues said:
Yes, but 3.3 V CMOS will produce legal TTL levels.

Jonathan
http://cq.cx/
Yes indeed. I think we've all satisfactorily surrounded the answer from all
directions and can go home happy. :)

Cheers.

Ken
 
P

Pooh Bear

Jan 1, 1970
0
Fred said:
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.

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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