3 WIRE SPI bi-directional communication

Question

Hello! 
 Does the SDK support a 3-wire SPI interface with bi-directional communication? 
 Like this:

Thanks!

ketiljo · Accepted Answer

No initially, but you can connect the MISO and MOSI pins externally with a resistor.

hmolesworth · Answer

Yes you can :-) This is a bare-metal example, but the same idea can be used with the Nordic drivers. Start in 3-wire command transmit; Send the command, then configure for 3-wire receive: // Send 3-wire whoami command byte (1 byte only) // Connect output drive, connect 1-wire rx/tx output to MOSI NRF_SPIM0->PSEL.MISO = 0xFFFFFFFF; // MISOPIN; NRF_SPIM0->PSEL.MOSI = MOSIPIN; NRF_GPIO->PIN_CNF[MOSIPIN] = 1; // output NRF_SPIM0->TXD.PTR = (uint32_t)spi3wTXBuf; NRF_SPIM0->TXD.MAXCNT = 1; NRF_SPIM0->RXD.PTR = NULL; NRF_SPIM0->RXD.MAXCNT = 0; NRF_SPIM0->EVENTS_ENDTX = 0; NRF_GPIO->OUTCLR = 1 << CSPIN; // drive cs low to initiate spi comm NRF_SPIM0->TASKS_START = 1; while(!NRF_SPIM0->EVENTS_ENDTX); // last byte transmitted // Manual says disable SPI before changing pins, but actually doesn't matter NRF_SPIM0->ENABLE = 0; // disable SPI // Disconnect output drive, connect 1-wire rx/tx input to MISO NRF_SPIM0->PSEL.MOSI = 0xFFFFFFFFUL; // MOSIPIN; NRF_GPIO->PIN_CNF[MOSIPIN] = 0; // input pin, input buffer connected, no pull, S0S1, sense disabled NRF_SPIM0->PSEL.MISO = MOSIPIN; // MISOPIN; NRF_SPIM0->ENABLE = 7; // enable SPI if it was disabled This works fine; on some SPI devices remember the internal 3-wire register mode has to be set first before reading.

3 WIRE SPI bi-directional communication

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