About SPI slave on 51422

[Elliot.Chao]

I use the SPI slave function on 51422. When I send a byte(0x31) to 51422 SPI slave from master, 51422 will back a byte (0xAA - DEF byte) to master. Why?

I send 0x31 every 1 seconds, but I always get 0xAA. Why??

[Håkon Alseth]

Hi,

That indicates that an ignored transaction has occurred (DEF register is set to '0xaa' in the SDK example).

1. Have you tried reducing the frequency on the SPIMaster side?
2. Do you always see this issue?
3. Are you sure that your SPIM is within the timing requirements stated for the SPIS module (PS chapter 8.3)?

Best regards Håkon

[Elliot.Chao]

1.Our master clock is 300kHZ 2.Yes 3.you mean "Serial Peripheral Interface Slave (SPIS) specifications" - SPIS timing diagram, one byte transmission, SPI Mode 0

[Håkon Alseth]

Have you set the same SPI mode on both sides? Could you try adding a delay of some microseconds after asserting the CSN line until you clock out data on MOSI?

BR Håkon

[Elliot.Chao]

Do you mean mode0~3 on 51422? I Set mode 0 OK,I will try to delay time.

But, I use 300KHZ clock from master, is it ok?

[Håkon Alseth]

Up to 2MHz is within spec and should be working. Yes, just make sure that both SPI-Master and Slave has the same SPI mode set. It might be that the SPIM clocks out data too fast after CSN is asserted, and adding a delay can work around this.

-H

[Elliot.Chao]

I use STM32 MCU for SPI master side and Nordic for SPI slave side. How can I mark sure that I send out the clock and data is consistent with Nordic? How can I know which mode I want to set it?

Thank you.