SPI three lines mode

[Zou]

I want to use the SPI in master mode, but the slave just have three lines,the miso and the mosi is the same line,but I don't know how to config the pins? Do the nRF52832 supports this mode? if YES,could you tell me how to use it or some examples to reference ?

[Wojtek]

you sure this is SPI? what is the name of the module?

[RK]

No the nRF52 (and the nRF51) don't support 3-wire SPI mode. Not that many chips do, it's not a very usual protocol. I did see a diagram somewhere (and it was Nordic-related) someone was using two resistors to join the MISO and MOSI of a standard SPI interface and hook it up to a 3-wire SPI slave. I wasn't entirely sure it would work.

[bjorn-spockeli]

Could sound like Maxim's 3-Wire/Microwire.

[atune]

Sorry for digging up an old question, but I just had to make a sensor with only "3-wire SPI" work with nRF52. Didn't see a similar answer (sorry if I missed it) and this seemed as good as any to blurt out my own solution.

devzone.nordicsemi.com/.../ is a hardware solution that should work as RK mentioned, but I had to preferably solve it in software.

A software solution that worked for me (reading a register) using the vanilla nrf_drv_spi:

1. (SPI is uninitialised when not in use)
2. Initialise SPI with MOSI as [SDIO_PIN] and MISO & CS as NRF_DRV_SPI_PIN_NOT_USED
3. Assert CS
4. Make a pure tx transfer (instance, tx_buf, tx_len, NULL, 0)
5. Uninitialise SPI
6. Initialise SPI with MISO as [SDIO_PIN] and MOSI & CS as NRF_DRV_SPI_PIN_NOT_USED
7. Make a pure rx transfer (instance, NULL, 0, rx_buf, rx_len)
8. Deassert CS
9. (Uninitialise SPI)

I guess some sensors might throw a hissy fit in between the transfers if there's too much delay, but at least I got it working with my own setup.

Anyhoo hope this helps someone in the same situation in the future.

[Bastien Reynard]

Worked for me too, thanks atune.