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STM32F302R8T6 Fanout capability

Question asked by haag.bill on May 10, 2017
Latest reply on May 10, 2017 by KIC8462852 EPIC204278916

Hello,

 

I'm using a STM32F302R8T6 in my project, and part of it's function is to be a SPI Master in a transmit only setup to a large amount of 74HC595 shift registers (45 in total).  Because I'm using a lot of shift registers, my main concern is "can my micro handle this much load/fan-out".  Now I've been researching fan-out, because I am not finding information about it in my micro-controllers datasheet, and I'm struggling quantifying what my actual load is going to be because of these 45 shift registers.

 

My high level layout is as follows: The shift registers will be placed on a circular board with a radius of ~3", the micro will be on a different "Controller" board, they will be connected by a cable roughly 8" long.

 

Below are my questions plainly stated:

 

1) How do I quantify what my fan-out/load is using 45 74HC595s to see if my micro can handle driving this?

2) Do I need to terminate the SPI Clock line at the end of the daisy chain or will the last shift register act as a termination feature?

3) Any other advice, or gotchas you all see are appreciated.

 

Thanks,

Bill

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