> On Thu, 29 Jul 2004 07:59:18 -0700, Harold Hallikainen
> <harold@hallikainen.com> wrote:
>> I've got an application where I'm driving 90 bicolor LEDs using a 180
>> bit
>> shift register (23 TC74VHC164FT) running at 3V. The SPI output of a PIC
>> is
>> driving this. Towards the far end of the shift register, I start getting
>> errors (bit offsets).
>
> I had the same problem with a 17C756A that was driving up to 21 x
> 74HC595s.  In the end I used 1 x 74HCT04 per 6 x 595s to sharpen the
> clock/data/strobe lines.  Did the trick quite nicely.
>
> Dan

     I'm not using an output latch, just letting the LEDs flicker a bit
during updates, so I don't have a stobe line. Since the data cascades
from one chip to the next, I'm not seeing how you're using the HCT04
on that line. On the clock lines, did you have the PIC drive the
inputs of several HCT04s, then have each output drive the clock input
of 6 shift registers (distributing the clock through the T04s)?
     As someone else suggested, I'll mess around with RC termination of
the clock line. I tried just an R to ground, and that pulled the
clock too low to drive the shift registers (this whole thing runs on
3V, so the PIC ouput current is a bit limited).

THANKS!

Harold

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