PGA970：PGA970通信 SPI异常

Hello Erbao,

Please note this is an English forum only. There is a Chinese forum which you can find here: https://e2echina.ti.com/ . If you wish for me to reply again, please continue in English, otherwise, please switch to the Chinese forum.

Putting your question through translate, it looks like you are struggling to talk with the PGA970 using SPI and are asking specifically about IF_SEL. 

I suggest you see my replies on this thread: https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/1225704/pga900-nothing-happens-when-trying-a-spi-connection 

To answer more directly, writing IF_SEL is not enough ensure SPI transactions go through. You also need to put the PGA970 (MCU) into reset. Please write to 1b to MICRO_RESET as well. As a result, the SPI transaction to the MICRO_CONTROLLER_INTERFACE register should be 0x3 to set MICRO_RESET and IF_SEL to 1b. The hyperlink has an example waveform of this.

If you do not use this method, you need to develop your own firmware to read the COMBUF registers after a COMBUF interrupt is triggered. More information can be found in this thread: https://e2e.ti.com/support/sensors-group/sensors---internal/f/sensors---internal-forum/1227357/pga900-agilent-lpsd-calibration-debug-questions/4636129#4636129 

Best,

-Cole