FS26 SPI communication

[vinaykl]

Hello Team,

I was trying to make FS26 SBC in Standby mode by sending 0xAA and 0x55 to FS_LP_REQ register. But SBC is not entering Standby mode. Kindly need your support in understanding. If possible please share me fs26 SPI communication document. How I can enter Standby mode in SBC?

Adding SPI communication, I tried to make SBC to enter Standby mode.

Thanx and regards,

Vinay

[JozefKozon]

Hello Vinaykl,

sending these two bytes alone is not enough. FS26 will reject the Standby request if one required condition is missing.

What must be done BEFORE sending 0xAA + 0x55

1. A valid wake‑up source must be enabled

If no wake‑up source is configured in M_WIO_CONFIG, FS26 refuses to enter Standby and returns to INIT_FS.
Allowed sources: WAKE1, WAKE2, GPIO1, GPIO2, LDT, or SPI wake‑up.

2. Command timing must be < 10 ms

Your timing looks correct, but FS26 requires strictly:

• First write: FS_LP_REQ = 0xAA

• Within 10 ms: FS_LP_REQ = 0x55

If the second command is late → FS26 jumps back to INIT_FS (not Standby).

3. Device must already be in INIT_FS or NORMAL mode

Standby request is ignored in:

• Debug mode

• Fail‑Safe mode

• Power‑up sequence

• If RSTB is low

• If ABIST/LBIST not completed

4. Your SPI frame must include the correct FS26 CRC

The image shows only the data bytes, but FS26 requires: 

[ M/FS | Address | R/W | Data_MSB | Data_LSB | CRC ]

Most likely reason in your capture: A wake‑up source is NOT enabled.

This is the most common reason:
Without a valid wake source, the FS26 will not enter Standby, even though 0xAA and 0x55 are correct. Please enable the wake up source in the M_WIO_CFG register. 

With Best Regards,

Jozef

[Henrik-Wires]

The SPI communication is covered in the datasheet

https://www.nxp.com/docs/en/data-sheet/FS26_SDS.pdf

15.6 SPI communication
15.5 Wake-up sources
16 Register mapping