Knowledge Base

Interface selection in SX1280

SX1280: I apologize for the obvious questions, but I can't find clear answers in the documentation.
What is the exact procedure for detecting the SPI or UART interface? How to make sure that the SPI interface has set up after the reset? What is the state of the interface lines (MISO, MOSI, SCK) during the reset (NRESET = 0) and immediately after (NRESET = 1)? What is the minimum NRESET signal time? What is the typical and maximum start time after reset (up to BUSY = 0)?
Hello Darek,
To use the SPI interface, you need to simply perform a single valid communication following reset of the device. (See the SPI timing diagram of the datasheet for details of a valid communication). The timing diagram also indicates the required states of the pins. Prior to reset you could set the interface to the pin states shown in table 14-2 of the datasheet. This would have the added benefit of optimising the radio consumption in SLEEP mode.

It does seem that the actual NRESET pulse duration is ambiguous. I am investigating this and will report back soon.

The only other thing to look out for is if your SPI bus is shared with multiple devices. Once you have performed a device reset – please make sure that you communicate first with the SX1280. We have seen a couple of cases where communication with other peripheral SPI devices has affected the interface selection. Note that once the SX1280 interface has been detected as SPI, you can share the bus with no problem.

Thanks, Tim
Hello Darek,

I can confirm that the minimum reset pulse time is 100 us.

Many Thanks, Tim