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Serial port power draw.

From: James Davidheiser <>
Date: Sat, 3 Mar 2001 12:33:25 -0500 (EST)

Question for the electronics savvy amongst you...

I am building a circuit to interface a PIC16C71 to a serial port.  My
initial plan was to use a MAX232A, but I have run across a stumbling
block.  On one specific design document (AN555 from microchip), there are
three circuits listed for doing the voltagelevel translations.  
One is a two chip design in which I'm not interested, one is a single chip
MAX232 based, and one is built up from basic components.  What threw a
monkey wrench at me was the fact that they specifically state that the
third (component-based) circuit is for powering directly off the serial
port, because of its low power draw.  They saw nothing about doing this
with the MAX232.  Does that mean I will need to power the MAX232 off of
something other than the serial port?  Does a max232 draw more power,
where it would exceed the spec of no more than 5mA?  A 16c71 draws about
2mA;  I can't expect that the MAX232 would draw more than 3, am I wrong?
Am I missing some other crucial point here?

James Davidheiser
Drexel University
Department of Physics

"Tell a man that there are 400 billion stars and he'll believe you"
"Say a bench has wet paint and he has to touch it"

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