From: shb*NO*SPAMemail@example.com (Si Ballenger)
Subject: Re: 74HC259 as a demultiplexer?
Date: Sat, 18 Jan 2003 06:24:32 GMT
Organization: maybe later...
NNTP-Posting-Date: Sat, 18 Jan 2003 06:24:38 +0000 (UTC)
X-Newsreader: Forte Free Agent 1.11/32.235
On Sat, 18 Jan 2003 00:04:50 -0500, Gary Tait
>On Sat, 18 Jan 2003 03:19:02 GMT, shb*NO*SPAMfirstname.lastname@example.org (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.
For testing I'm using 4 D cells at ~5.5v. On the parallel port
data pin, I only need to power the chip logic, and have the chip
send ~1ma on an output to a transistor. Hopefully the chip itself
doesn't take much power to operate.