piclist 2001\01\19\112932a >
Thread: Need 74HC165 with tristate output
www.piclist.com/techref/ios.htm?key=output
face picon face BY : Alan B. Pearce email (remove spam text)



>I'm starting a project in which a number of inputs (>16) need to
>be periodically read via the SSP (SPI) bus.  In the beginning it
>looked like using a few 74HC165A's would be just the thing,
>until I realized that the outputs are not tristate.  Thus I can't
>tie multiple outputs together onto the SDI line :-(
>Can anyone suggest a chip with a similar function that DOES
>have a tristate output?

Why do they need to tri-state? these are parallel load serial out registers
which are surely what you need. I would have thought that you would hook Q7 (or
is it Qh on your datasheet) to the serial in line of the next chip. The last
chip has its Q? pin hooked to the SPI in pin on the PIC. Once you move the
shift/load pin on the 165's from load to shift, then the clock of the SPI will
serially shift the data into the pic.

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