Can I link 2 Nanos via SPI using just 2/3 wires?

Projects Networking, Protocols, and Devices
1

I have 2 Nanos which I want to link together.
One is the master and only writes to the other, it never needs to read.

Is there a way to use the standard SPI libraries to link them using 2/3 wires?
(My understanding if the library expects 4 pins to be defined. Can I avoid this?)

I only have 2 (I could free up a 3rd one but would rather not) pins free.
Thanks

2

You will need 3 on the Master
Clock, Data (MOSI), Chip Select
and 3 on the Slave
Clock, Data (MOSI), Chip Select

(Yes, MOSI to MOSI)

Nick Gammon has a good page with examples here

3

CrossRoads:
You will need 3 on the Master
Clock, Data (MOSI), Chip Select
and 3 on the Slave
Clock, Data (MOSI), Chip Select

(Yes, MOSI to MOSI)

Nick Gammon has a good page with examples here
Gammon Forum : Electronics : Microprocessors : SPI - Serial Peripheral Interface - for Arduino

Thanks CrossRoads, That page was very handy, and I've got it working fine with 3 wires.

4

I am curious why I can't just tie the SS line on the receiver to ground.

If I disconnect it whilst it running, it keeps working just fine.
But if I reboot both boards, the link seems to fail and won't start

Can anyone explain why?

5

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