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RM0367 Rev 7 737/1043

RM0367 Inter-integrated circuit (I2C) interface

763

Figure 237. Transfer bus diagrams for SMBus slave transmitter (SBC=1)

SMBus Slave receiver

When the I2C is used in SMBus mode, SBC must be programmed to ‘1’ in order to allow the

PEC checking at the end of the programmed number of data bytes. In order to allow the

ACK control of each byte, the reload mode must be selected (RELOAD=1). Refer to Slave

byte control mode on page 710 for more details.

In order to check the PEC byte, the RELOAD bit must be cleared and the PECBYTE bit

must be set. In this case, after NBYTES-1 data have been received, the next received byte

is compared with the internal I2C_PECR register content. A NACK is automatically

generated if the comparison does not match, and an ACK is automatically generated if the

comparison matches, whatever the ACK bit value. Once the PEC byte is received, it is

copied into the I2C_RXDR register like any other data, and the RXNE flag is set.

In the case of a PEC mismatch, the PECERR flag is set and an interrupt is generated if the

ERRIE bit is set in the I2C_CR1 register.

If no ACK software control is needed, the user can program PECBYTE=1 and, in the same

write operation, program NBYTES with the number of bytes to be received in a continuous

flow. After NBYTES-1 are received, the next received byte is checked as being the PEC.

Caution: The PECBYTE bit has no effect when the RELOAD bit is set.

MS19869V2

Example SMBus slave transmitter 2 bytes + PEC,

EV1: ADDR ISR: check ADDCODE, program NBYTES=3, set PECBYTE, set ADDRCF

EV2: TXIS ISR: wr data1

EV3: TXIS ISR: wr data2

ADDR

legend:

transmission

reception

SCL stretch

EV1 EV2

TXIS

EV3

NBYTES 3

S Address A Adata1

data2

PEC

ST STM32L0x3 User Manual

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