ST STM32WL55JC Reference Manual page 1090

Inter-integrated circuit (I2C) interface
Caution: The PECBYTE bit has no effect when the RELOAD bit is set.
Figure 299. Transfer sequence flowchart for SMBus slave transmitter N bytes + PEC
Figure 300. Transfer bus diagrams for SMBus slave transmitter (SBC=1)
Example SMBus slave transmitter 2 bytes + PEC,
NBYTES
EV1: ADDR ISR: check ADDCODE, program NBYTES=3, set PECBYTE, set ADDRCF
EV2: TXIS ISR: wr data1
EV3: TXIS ISR: wr data2
1090/1454
No
Read ADDCODE and DIR in I2C_ISR
I2C_CR2.NBYTES = N + 1
Write I2C_TXDR.TXDATA
ADDR TXIS TXIS
S Address A data1
EV1 EV2
EV3
SMBus slave
transmission
Slave initialization
I2C_ISR.ADDR =
1?
Yes
PECBYTE=1
Set I2C_ICR.ADDRCF
No
I2C_ISR.TXIS
=1?
Yes
A data2 A PEC
3
RM0453 Rev 2
SCL
stretched
MS19867V2
legend:
transmission
reception
SCL stretch
NA P
RM0453
MS19869V2