RM0090 Inter-integrated circuit (I
2
C) interface
Doc ID 018909 Rev 4 728/1422
25.5 I
2
C debug mode
When the microcontroller enters the debug mode (Cortex™-M4F core halted), the SMBUS
timeout either continues to work normally or stops, depending on the
DBG_I2Cx_SMBUS_TIMEOUT configuration bits in the DBG module. For more details,
refer to Section 33.16.2: Debug support for timers, watchdog, bxCAN and I2C on
page 1396.
25.6 I
2
C registers
Refer to Section 1.1 on page 47 for a list of abbreviations used in register descriptions.
The peripheral registers can be accessed by half-words (16 bits) or words (32 bits).
25.6.1 I
2
C Control register 1 (I2C_CR1)
Address offset: 0x00
Reset value: 0x0000
15141312111098 7 6543210
SWRST
Res.
ALERT PEC POS ACK STOP START
NO
STRETCH
ENGC ENPEC ENARP
SMB
TYPE
Res.
SMBUS 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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