NXP Semiconductors MC9S08SU16 Reference Manual page 367

Field
0 Disabled
1 Enabled
5 Master Mode Select
MST
When MST is changed from 0 to 1, a START signal is generated on the bus and master mode is selected.
When this bit changes from 1 to 0, a STOP signal is generated and the mode of operation changes from
master to slave.
0 Slave mode
1 Master mode
4 Transmit Mode Select
TX
Selects the direction of master and slave transfers. In master mode this bit must be set according to the
type of transfer required. Therefore, for address cycles, this bit is always set. When addressed as a slave
this bit must be set by software according to the SRW bit in the status register.
0 Receive
1 Transmit
3 Transmit Acknowledge Enable
TXAK
Specifies the value driven onto the SDA during data acknowledge cycles for both master and slave
receivers. The value of SMB[FACK] affects NACK/ACK generation.
NOTE: SCL is held low until TXAK is written.
0 An acknowledge signal is sent to the bus on the following receiving byte (if FACK is cleared) or the
current receiving byte (if FACK is set).
1 No acknowledge signal is sent to the bus on the following receiving data byte (if FACK is cleared) or
the current receiving data byte (if FACK is set).
2 Repeat START
RSTA
Writing 1 to this bit generates a repeated START condition provided it is the current master. This bit will
always be read as 0. Attempting a repeat at the wrong time results in loss of arbitration.
1 Wakeup Enable
WUEN
The I2C module can wake the MCU from low power mode with no peripheral bus running when slave
address matching occurs.
0 Normal operation. No interrupt generated when address matching in low power mode.
1 Enables the wakeup function in low power mode.
0 This field is reserved.
Reserved This read-only field is reserved and always has the value 0.
NXP Semiconductors
I2C_C1 field descriptions (continued)
MC9S08SU16 Reference Manual, Rev. 5, 4/2017
Chapter 21 Inter-Integrated Circuit (I2C)
Description
367