> I have built an 8 x 128 leds designs as a matrix display,
> the rows [8] goes to rb0  to rb7 then the columns goes to the
> ra0 to ra3 through a cascade demultiplexer

It sounds very similar to mine, except I use transistors for
drive. Without them it would be very dim. I have to disagree
slightly with others' comments about the required power.
Although this uses normal 3mm LEDs it is quite bright and
uses only 40mA (surprised me !!)  For 5mm ultrabrights, I
agree, the power consumed will be higher, but what I found
illustrates that it can be done at lower power (battery supply
was a requirement). This one is strobing at 200Hz, based
on a timer IRQ. It's a work in progress (displays messages
but the s/w is unrefined), so can't help much further

http://home.clear.net.nz/pages/joecolquitt/message.html

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