# SPI wiring SDIO pin with MISO and MOSI

I'm connecting the N76E003AT20 microcontroller to an RF module. The N76E003AT20 has 4 SPI pins: SPCLK, MISO, MOSI and SS. The module also has 4 SPI pins which are SCLK, SDIO, CSB and FCSB as shown in the table:

I understand that I have to connect SCLK and SPCLK. Do I connect SDIO to both MISO and MOSI? How about CSB and FCSB?

• Which module? The uC will be the master, I guess. I that case, you usually don't care about the SS pin.connecting MISO and MOSI together sound wrong, then the master will receice what he just sent or there will be bus contention Dec 23, 2020 at 17:40

It appears that this RF module doesn't exactly follow the SPI specification. This means that you probably won't be able to use a canned high-level driver. Some of this is speculation based on a SPI slave module that I found that uses a bidirectional data signal.

SPI Slave Selects (AKA Chip Selects) are basically simple MCU outputs, so creating a second SS should be easy.

Connecting MISO and MOSI also causes complications, you must tri-state MOSI during the part of the cycle when the slave is driving SDIO.

MPU        SLAVE
SPCLK      SCLK
MISO/MOSI  SDIO
SS1        CSB
SS2        FCSB

• Thank you! If I connect MOSI to SDIO through say a 10k resistor and then connect MISO directly to SDIO, will that do the trick? Dec 24, 2020 at 12:32
• Yes, you may be able to use a resistor so that the slave can overdrive the signal. Dec 24, 2020 at 16:38