MSP430FR2355: Half duplex SPI on MOSI/MISO --- Can I do this?

Steve Wenner

Part Number: MSP430FR2355

I am using a Microchip digital potentiometer which shares the MISO/MOSI line and works on half duplex SPI communication. I am using the above EVM and would like to run SPI to do this....Does anyone know if '3-pin' SPI as TI calls it works in this manner? UG section 23.2

Thanks

Steve

over 2 years ago

0 Steve Wenner over 2 years ago

Genius 3190 points

I've seen where MOSI/MISO can be tied together with a 10k ohm resistor to avoid conflict

0 Bruce McKenney47378 over 2 years ago

Guru 88720 points

This is commonly called "3-wire" mode (/CS, SCK, MISO+MOSI). The EUSCI "3-pin" mode (SCK, MISO, MOSI) is a different thing.

The EUSCI doesn't know about 3-wire mode. You can use 3-pin mode (with /CS via a GPIO) to talk to a 3-wire slave. (You can also use 4-pin mode, but the way it does the /CS is not useful for most slaves.) You'll have to do the line reversals in your code, using the PSEL bit.

There's a suggested procedure here:

https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/1005190/msp430f1101a-3-wire-spi-cs-sck-mosi-miso

0 Steve Wenner over 2 years ago in reply to Bruce McKenney47378

Genius 3190 points

Thanks Bruce.....

Decided to go with another digital pot that has independent SDO / SDI

Steve

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MSP430FR2355: Half duplex SPI on MOSI/MISO --- Can I do this?