At 05:15 AM 1/16/2004, Lucian Copat wrote:
>Hello to all Piclisters,
>
>I am designing a circuit which uses 3 shift-registers to spare some
>microcontroller inputs. I actually use 74HC165 as a shift register, but
>I found also CD4021. In practice, I found out that the data pin of each
>register cannot be tied to a common data bus. Is there a solution to do
>this ? (for 3 shift-registers, tie the Q7 data out pin to the same data
>bus D0 pin, which is also common to other circuits).

The shift registers are daisy-chained: the serial data out of one device
connects to the serial data input of the next.  You mention CD4021: ground
the 1st device's DS input (pin 11), connect Q8 (pin 3) of that chip to the
DS input of the 2nd chip, and so on.  The last chip's Q8 pin goes to the
PIC.  Connect all the clock pins together and to the PIC, do the same for
the P/S lines.  To use: pulse the P/S line high to load the shift registers
with the parallel data, then clock the data out.

dwayne

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Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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