ST STM32F301 6 Series Reference Manual page 692

Inter-integrated circuit interface (I2C)
SMBus controller receiver
When the SMBus controller wants to receive, at the end of the transfer, the PEC followed by
a STOP condition, the automatic end mode can be selected (AUTOEND = 1). The
PECBYTE bit must be set and the target address programmed before setting the START bit.
In this case, after the receipt of NBYTES[7:0] - 1 data bytes, the next received byte is
automatically checked versus the I2C_PECR register content. A NACK response is given to
the PEC byte, followed by a STOP condition.
When the SMBus controller receiver wants to receive, at the end of the transfer, the PEC
byte followed by a RESTART condition, the software mode must be selected (AUTOEND =
0). The PECBYTE bit must be set and the target address programmed before setting the
START bit. In this case, after the receipt of NBYTES[7:0] - 1 data bytes, the next received
byte is automatically checked versus the I2C_PECR register content. The TC flag is set
after the PEC byte reception, stretching the SCL line low. The RESTART condition can be
programmed in the TC interrupt subroutine.
Caution: The PECBYTE bit has no effect when the RELOAD bit is set.
692/874 RM0366 Rev 5
RM0366