3-wire Interface on nRF52?

[jcondon]

One of the features missing on the nRF51 was the 3-wire SPI interface standard (Clk, Data, CS). Is this available for the nRF52?

[Anders Strand]

Hi.

The nRF52 will not have built in support for combining the MISO and MOSI line. If you are using a 3-wire device, you can connect MOSI to MISO with a 10k resistor like this guide does.

-Anders

[jcondon]

That's too bad. It would be nice to get those IO back.

[wdu]

This information is not correct. At least the SPI block supports 3-wire SPI (combined MISO/MOSI), and I suspect the SPIM block also supports it.

[jcondon]

wdu, where are you seeing 3-wire SPI support (w/ combined MISO/MOSI?). On the product specification I see 3 distinct pins for CLK, MISO, and MISO not the two pins required (CLK & MISO/MOSI). There is also nowhere I can find in the SPIM block that mentions it.

[wdu]

Set MISO or MOSI to disconnected (0xffffffff) while doing write resp read. Reconfigure the SPI block as needed while keeping CS asserted when the IO direction has to change. Since most SPI devices I know will require no or one direction change per command, you'd have to split the transaction in at most two parts. I do this with the SPI block, haven't worked with SPIM yet.