I2C Slave Mode; Table 139. I2C Configuration Table - STMicroelectronics RM0365 Reference Manual

Inter-integrated circuit (I2C) interface
When RELOAD=0 in master mode, the counter can be used in 2 modes:
•
Automatic end mode (AUTOEND = '1' in the I2C_CR2 register). In this mode, the
master automatically sends a STOP condition once the number of bytes programmed
in the NBYTES[7:0] bit field has been transferred.
• Software end mode (AUTOEND = '0' in the I2C_CR2 register). In this mode, software
action is expected once the number of bytes programmed in the NBYTES[7:0] bit field
has been transferred; the TC flag is set and an interrupt is generated if the TCIE bit is
set. The SCL signal is stretched as long as the TC flag is set. The TC flag is cleared by
software when the START or STOP bit is set in the I2C_CR2 register. This mode must
be used when the master wants to send a RESTART condition.
Caution: The AUTOEND bit has no effect when the RELOAD bit is set.
Master Tx/Rx NBYTES + STOP
Master Tx/Rx + NBYTES + RESTART
all received bytes ACKed
Slave Rx with ACK control
28.4.7

I2C slave mode

I2C slave initialization
In order to work in slave mode, the user must enable at least one slave address. Two
registers I2C_OAR1 and I2C_OAR2 are available in order to program the slave own
addresses OA1 and OA2.
•
OA1 can be configured either in 7-bit mode (by default) or in 10-bit addressing mode by
setting the OA1MODE bit in the I2C_OAR1 register.
OA1 is enabled by setting the OA1EN bit in the I2C_OAR1 register.
•
If additional slave addresses are required, the 2nd slave address OA2 can be
configured. Up to 7 OA2 LSB can be masked by configuring the OA2MSK[2:0] bits in
the I2C_OAR2 register. Therefore for OA2MSK configured from 1 to 6, only OA2[7:2],
OA2[7:3], OA2[7:4], OA2[7:5], OA2[7:6] or OA2[7] are compared with the received
address. As soon as OA2MSK is not equal to 0, the address comparator for OA2
excludes the I2C reserved addresses (0000 XXX and 1111 XXX), which are not
acknowledged. If OA2MSK=7, all received 7-bit addresses are acknowledged (except
reserved addresses). OA2 is always a 7-bit address.
These reserved addresses can be acknowledged if they are enabled by the specific
enable bit, if they are programmed in the I2C_OAR1 or I2C_OAR2 register with
OA2MSK=0.
OA2 is enabled by setting the OA2EN bit in the I2C_OAR2 register.
• The General Call address is enabled by setting the GCEN bit in the I2C_CR1 register.
When the I2C is selected by one of its enabled addresses, the ADDR interrupt status flag is
set, and an interrupt is generated if the ADDRIE bit is set.
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Table 139. I2C configuration table

Function
Slave Tx/Rx
DocID025202 Rev 7
SBC bit RELOAD bit
x 0
x 0
0 x
1 1
RM0365
AUTOEND bit
1
0
x
x