SPIS Receive Data error

[Jason]

Hi,Nordic:

I use an STM32 to communication with nRF51822 through SPI, and i set the STM32 to master,the nRF51822 to SPI slave, 51822 works as SPIS.

When STM32 send a frame of date to 51822,and the 51822 replies a frame of data. I find that the STM32 receives a data of DEF (default) character as the RM: "The SPI slave will try to acquire the semaphore when CSN goes low. If the SPI slave does not manage toacquire the semaphore at this point, the transaction will be ignored. This means that all incoming data onMOSI will be discarded, and the DEF (default) character will be clocked out on the MISO line throughout the whole transaction. "

My question is : how the master know the time to send data to 51822 to avoid this error, thank you.

[Sami]

Hi Jason, I had a similar problem and I tried to solve it by one GPIO connected to Master but still it happen sometime that Master received DEF character. The issue is that the best time for sending data from Master is the time that SPIS release the semaphore and since the shortcut is used, there is no any way to find this time.