Multiple SPI clients on base board

WisBlock
1

Question

How can I use multiple SPI parts on the same base board without introducing chip select conflicts?

Environment

The parts in use are:

  • RAK19007 base board
  • RAK4631 MCU module
  • RAK15001 flash storage
  • RAK14014 display module

The connected computer is a Ubuntu 24.04.1 Desktop (AMD64.)

Concern

I think that the chip select (CS) connections of the RAK15001 flash storage are the same as those on the RAK14014 display module, and would cause conflicts on the SPI bus.

Notes

I assume that by modifying the hardware on one of the two RAK modules, I can change the chip select connection to use an alternate chip select pin on the MCU.

If this is the correct approach, then would somebody please guide me to understand how to modify the hardware?

2

Some important advice is found in the datasheets, where the schematic diagrams are found at the bottom of the pages.

I don’t understand if the indicated CS and SPI_CS labels are the same electrical connection, or if they are two different connections to the MCU.

3

You can check with our WisBlock Pin Mapper for conflicts.

The problem is that both the RAK15001 and the RAK14014 are using the same signal for the CS.
And you cannot change the CS on either of the boards.

This combination will not work.

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4

Okay thanks @beegee for confirming the CS conflict when using both RAK15001 and RAK14014 on the same RAK base board. It’s really too bad that this problem has no solution.

I guess I will keep the LCD module, discard the flash module, and obtain no more modules that use SPI.

5

It’s more expensive, but if you are ok with a smaller size, the FRAM modules could be an alternative. The smaller ones have I2C interface. E.g. RAK15004