piclist 2001\01\19\151724a >
Thread: RA4 as output attached to TTL logic, pull-up minimum consumption
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face BY : Dwayne Reid email (remove spam text)



At 11:06 AM 1/19/01 +0100, Jeszs wrote:
>Dear piclisters,
>
>I am using RA4 as output pin to attack a TTL chip. Most of the time this
>pin shall be 0 V.
>
>Since RA4 is open drain output, I need some kind of pull-up circuit.
>Frequency is not an issue but could be in the future.
>The basic pull-up resistor would be continuously consuming energy and this
>is what I see 'ugly' in my design.

Are you using 'real' TTL?  If so, TTL inputs normally float HI and consume
about 1 mA then pulled LO.  In other words, the current consumption from a
pullup resistor is minor compared to the quiescent current consumed by your
TTL logic.

If you *are* using real TTL, use a pullup resistor of 4.7K - its gonna cost
you 1 mA.  If you are using LS TTL, go to 10K.  If using HC, go to 100K.

dwayne



Dwayne Reid   <STOPspamdwayner@spam@spamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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Subject (change) RA4 as output attached to TTL logic, pull-up minimum consumption

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