I have multiplexed 4 x 7 segment displays.

I used 220R resistors in series with the segments and these are
driven directly from the port pins. Each display common was controlled by a
BC547 transistor with a 4K7 base resistor. (Common cathode displays).

The IRQ which updated the displays was set to 5mS. So each display is
on for 5mS and off for 15mS.  25% duty cycle. The display brightness
is good even under fluro lighting. The chip is running at 10MHz.

In the IRQ, all displays are turned off for 5 NOP's, then change
digit data, another 5 NOP's, then the next display in the sequence is turned on.

This works fine for my application.

Regards

Tony


Just when I thought I knew it all,
I learned that I didn't.