Re: [CAD_CAM_EDM_DRO] Re: ParPort output low - hi-Z or ground?

ghidera2000 wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ghidera2000" > Oh and
>thanks for the 3.3 volt tip. I checked mine and the outputs
>
>
>>are 3.3v while the input high is a full 5v. Had to adjust the led
>>resistors (7mA just ain't enough).
>>
>>
>
>Actually, I should never post before I have my morning coffee...
>3.3V on outputs doesn't affect my on-state LED current...
>
>However, I'm supplying +5 from the floppy connector to the leds and
>the port "off" state (off to my circuit operation anyway) is 3.3v...
>I still have current flowing to the parallel port... Hmmmmm
>
>
>

LEDs usually drop about 1.6 Volts when conducting. 5 V - 1.6 = 3.4 V
So, if the anode of the LED is at 5 V and the cathode is at 3.3 V, and there
is some resistor there to limit current, the current in the LED will be
minute. So, this will still work OK. The 3.3 V may be about normal
for a TTL output pulling to logic 1, anyway, although they usually pull
up closer to 3.6 V, when run from a 5V supply. The inputs probably have
a real resistor that pulls all the way up to +5 V.

Jon