RM0401 Rev 3 613/771
RM0401 Inter-integrated circuit (I
2
C) interface
626
23.5 I
2
C debug mode
When the microcontroller enters the debug mode (Cortex
®
-M4 with FPU core halted), the
SMBUS timeout either continues to work normally or stops, depending on the
DBG_I2Cx_SMBUS_TIMEOUT configuration bits in the DBGMCU module. For more
details, refer to Section 26.16.2: Debug support for timers, watchdog, and I2C.
23.6 I
2
C registers
Refer to Section 1.2 on page 34 for a list of abbreviations used in register descriptions.
The peripheral registers have to be accessed by half-words (16 bits) or words (32 bits).
23.6.1 I
2
C Control register 1 (I2C_CR1)
Address offset: 0x00
Reset value: 0x0000
1514131211109876543210
SW
RST
Res. ALERT PEC POS ACK STOP START
NO
STRET
CH
ENGC ENPEC ENARP
SMB
TYPE
Res.
SM
BUS
PE
rw rw rw rw rw rw rw rw rw rw rw rw rw rw
Bit 15 SWRST: Software reset
When set, the I2C is under reset state. Before resetting this bit, make sure the I2C lines are
released and the bus is free.
0: I
2
C Peripheral not under reset
1: I
2
C Peripheral under reset state
Note: This bit can be used to reinitialize the peripheral after an error or a locked state. As an
example, if the BUSY bit is set and remains locked due to a glitch on the bus, the
SWRST bit can be used to exit from this state.
Bit 14 Reserved, must be kept at reset value
Bit 13 ALERT: SMBus alert
This bit is set and cleared by software, and cleared by hardware when PE=0.
0: Releases SMBA pin high. Alert Response Address Header followed by NACK.
1: Drives SMBA pin low. Alert Response Address Header followed by ACK.
Bit 12 PEC: Packet error checking
This bit is set and cleared by software, and cleared by hardware when PEC is transferred or
by a START or Stop condition or when PE=0.
0: No PEC transfer
1: PEC transfer (in Tx or Rx mode)
Note: PEC calculation is corrupted by an arbitration loss.
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