At 09:58 AM 9/14/2003 -0400, you wrote:
>At 01:13 AM 9/15/2003 +1200, you wrote:
>> > this problem.  If I am understanding correctly, you load the
>> > chain of serial-in / parallel-out shift registers with one row
>> > of LED data at a time, then light the LEDs by enabling the
>> > row
>>
>>Yes, the array "scans" like lines on a TV screen. The row
>>timing is based on a 200Hz timer IRQ => 200 / 7 refreshes
>>per row per second, which is a little slower than I'd like but
>>isn't very noticeable (and it is a work in progress - I think I'd
>>revisit the thing armed with a grunty F452 or Scenix). One
>>very bad consequence of too slow a refresh rate is that
>>letters appear to slope as they move. It looks horrible
>
>Hardware SPI can get the data out to the SRs pretty fast...

P.S. I suggest using SRs with an output latch such as the HC594/595.
Then the shifting time doesn't cut into the duty cycle, just processor
bandwidth. You can get a 5MHz bit rate with a 20MHz PIC, so 64 bits in
a couple of tens of microseconds. If you devote 20-25% of the processor
bandwidth to refreshing the display you should be able to get > 1kHz
refresh rate for the entire display using a PIC. Maybe use a 5kHz interrupt.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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