Other Parts Discussed in Thread: LP87745-Q1
I am working with the custom board where IWR6843 is connected with LP87745-Q1 PMIC via SPI.
When I am trying to write on the PMIC user register on address 0x0A with data 0x9B to unlock the register, I am getting unexpected behavior from CS signal and hence the write is not successful.
After writing 0x9B on address 0x0A I am expecting 0x10EF00 as response on SDO line whereas I am getting 0x101010, which just first byte getting repeated two times.
I am guessing its because after every 8-bit CS is going high for few micro seconds and thats why maybe PMIC is understanding it as end of transmission and sending again same first byte.
For SPI I am using data size 8 bit here.
Below is the signal pattern observed on oscilloscope
Expected behaviour from SPI driver when writing to PMIC.
The above diagram is from the complete datasheet of LP87754.
It is the same behavior while reading as well from the user register address.
When using 8-bit data size I could read only the first byte 0x10. Whereas when I use 16-bit data size I could read 0x10EF but not the third byte. The same two bytes get repeated again.
Not sure if it's the problem with SPI driver behavior here.
Thanks and Regards,