From: Gary Tait
Subject: Re: 74HC259 as a demultiplexer?
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Date: Sat, 18 Jan 2003 00:04:50 -0500
NNTP-Posting-Date: Sat, 18 Jan 2003 00:07:05 EST
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On Sat, 18 Jan 2003 03:19:02 GMT, shb*NO*SPAMemail@example.com (Si
>I'm trying to use a 74HC259 chip as a simple demultiplexer
>connected to the parallel port data pins. What I wuld like to do
>is use the 5v from one data pin to power the chip, and use three
>other data pins as the 3 logic inputs (A0-A2). The chip can
>perform several functions, but I just need the output lines
>(Q0-Q7) on the chip to go to 5v depending on which of the 3 input
>lines is at 5v. Looking at the function table in the below data
>sheet, I would think to set the chip for this type of operation,
>MR and LE lines would need to be connected to ground to keep them
>low. Also, the D line would need to be connected to to Vcc to
>keep it high. In this configuration I expected the output lines
>to go high when combinations of the input lines are made high by
>connecting them to Vcc. This doesn't seem to work (after
>tinkering, I may need to use a "fresh" chip), so does anybody see
>anything obvious in this setup that would not let this work?
>Currently I'm just powering it with a couple of batterys to see
>if it will work. Any info on this would be much appreciated!
What is your power coniguration? 4 AAs should be enough. I'd use
diodes to feed from more than one port pin, if not using an
independant power source.