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Re: Parallel Card
- Subject: Re: Parallel Card
- From: "Michael J. Mahon" <mjmahon@aol.com>
- Date: Thu, 25 May 2006 12:30:31 -0700
- In-reply-to: <pz0dg.84082$H71.19448@newssvr13.news.prodigy.com>
- Newsgroups: comp.sys.apple2
- References: <pz0dg.84082$H71.19448@newssvr13.news.prodigy.com>
- Reply-to: mjmahon@aol.com
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Bryan Parkoff wrote:
Can you please recommend which brand is better for parallel card so I
can buy two parallel cards. I use both parallel cards installed on slot 1
and slot 2 to test 16 LEDs.
If the problem is just driving LEDs, then an 8-bit parallel output port
can easily drive 40 LEDs in a 5x8 matrix.
Three bits of the output port are decoded by a 74LS138 decoder, which
drives eight "column" transistors, while the remaining 5 output bits
drive five "row" transistors.
The 40 (or less) LEDs are then controlled by multiplexing at a 50Hz
or higher rate by sending the column number and row bits in sequence
to the 8-bit parallel port.
-michael
Music synthesis for 8-bit Apple II's!
Home page: http://members.aol.com/MJMahon/
"The wastebasket is our most important design
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