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Shift registers parrallel to serial: do I need to ungroup them ?

Question asked by prieur.jean on May 22, 2013
Latest reply on May 31, 2013 by prieur.jean

I'm working on an interface based on STM32F407 with 48 buttons. I use 74HC165 shift registers parrallel in/serial out to multiplex my buttons states.

I need to cascading 6 registers to connect the 48 buttons.

This is my question: is it preferable to cascading the 6 registers or to "ungroup" them and cascading them 3 by 3 ? I mean, 3 registers are chained and communicate with the microcontroller, and 3 others registers are chained and communicate with the microcontroller with another pins.

What is the best way to optimize the communication speed ?