I2Cx_C1 field descriptions (continued)Field DescriptionSelects the direction of master and slave transfers. In master mode this bit must be set according to thetype of transfer required. Therefore, for address cycles, this bit is always set. When addressed as a slavethis bit must be set by software according to the SRW bit in the status register.0 Receive1 Transmit3TXAKTransmit Acknowledge EnableSpecifies the value driven onto the SDA during data acknowledge cycles for both master and slavereceivers. The value of the FACK bit 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 thecurrent 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) orthe current receiving data byte (if FACK is set).2RSTARepeat STARTWriting a one to this bit generates a repeated START condition provided it is the current master. This bitwill always be read as zero. Attempting a repeat at the wrong time results in loss of arbitration.1WUENWakeup EnableThe I2C module can wake the MCU from low power mode with no peripheral bus running when slaveaddress matching occurs.0 Normal operation. No interrupt generated when address matching in low power mode.1 Enables the wakeup function in low power mode.0DMAENDMA EnableThe DMAEN bit enables or disables the DMA function.0 All DMA signalling disabled.1 DMA transfer is enabled and the following conditions trigger the DMA request:• While FACK = 0, a data byte is received, either address or data is transmitted. (ACK/NACKautomatic)• While FACK = 0, the first byte received matches the A1 register or is general call address.If any address matching occurs, IAAS and TCF are set. If the direction of transfer is known frommaster to slave, then it is not required to check the SRW. With this assumption, DMA can also beused in this case. In other cases, if the master reads data from the slave, then it is required to rewritethe C1 register operation. With this assumption, DMA cannot be used.When FACK = 1, an address or a data byte is transmitted.Chapter 38 Inter-Integrated Circuit (I2C)KL25 Sub-Family Reference Manual, Rev. 3, September 2012Freescale Semiconductor, Inc. 693
