ST STM32F412 Reference Manual page 710

Fast-mode Plus Inter-integrated circuit (FMPI2C) interface
Bits 31:27 Reserved, must be kept at reset value.
Bit 26 PECBYTE: Packet error checking byte
Note: Writing '0' to this bit has no effect.
Bit 25 AUTOEND: Automatic end mode (master mode)
Note: This bit has no effect in slave mode or when the RELOAD bit is set.
Bit 24 RELOAD: NBYTES reload mode
Bits 23:16 NBYTES[7:0]: Number of bytes
Note: Changing these bits when the START bit is set is not allowed.
Bit 15 NACK: NACK generation (slave mode)
Note: Writing '0' to this bit has no effect.
Bit 14 STOP: Stop generation (master mode)
Note: Writing '0' to this bit has no effect.
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This bit is set by software, and cleared by hardware when the PEC is transferred, or when a
STOP condition or an Address matched is received, also when PE=0.
0: No PEC transfer.
1: PEC transmission/reception is requested
This bit has no effect when RELOAD is set.
This bit has no effect is slave mode when SBC=0.
If the SMBus feature is not supported, this bit is reserved and forced by hardware to '0'.
Refer to Section 23.3: FMPI2C
This bit is set and cleared by software.
0: software end mode: TC flag is set when NBYTES data are transferred, stretching SCL low.
1: Automatic end mode: a STOP condition is automatically sent when NBYTES data are
transferred.
This bit is set and cleared by software.
0: The transfer is completed after the NBYTES data transfer (STOP or RESTART follows).
1: The transfer is not completed after the NBYTES data transfer (NBYTES is reloaded). TCR
flag is set when NBYTES data are transferred, stretching SCL low.
The number of bytes to be transmitted/received is programmed there. This field is don't care
in slave mode with SBC=0.
The bit is set by software, cleared by hardware when the NACK is sent, or when a STOP
condition or an Address matched is received, or when PE=0.
0: an ACK is sent after current received byte.
1: a NACK is sent after current received byte.
This bit is used in slave mode only: in master receiver mode, NACK is automatically
generated after last byte preceding STOP or RESTART condition, whatever the NACK
bit value.
When an overrun occurs in slave receiver NOSTRETCH mode, a NACK is
automatically generated whatever the NACK bit value.
When hardware PEC checking is enabled (PECBYTE=1), the PEC acknowledge value
does not depend on the NACK value.
The bit is set by software, cleared by hardware when a STOP condition is detected, or when
PE = 0.
In Master Mode:
0: No Stop generation.
1: Stop generation after current byte transfer.
implementation.
RM0402 Rev 6
RM0402