26.5.4 Master Control B
| Name: | MCTRLB |
| Offset: | 0x04 |
| Reset: | 0x00 |
| Property: | - |
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
| FLUSH | ACKACT | MCMD[1:0] | |||||||
| Access | R/W | R/W | R/W | R/W | |||||
| Reset | 0 | 0 | 0 | 0 | |||||
Bit 3 – FLUSH Flush
Writing a ‘1’ to this bit generates a strobe for one clock cycle disabling and then enabling the master.
Writing ‘0’ has no effect.
The purpose is to clear the internal state of the master: For TWI master to transmit successfully, it is recommended to write the Master Address register (TWIn.MADDR) first and then the Master Data register (TWIn.MDATA).
The peripheral will transmit invalid data if TWIn.MDATA is written before TWIn.MADDR. To avoid this invalid transmission, write ‘1’ to this bit to clear both registers.
Bit 2 – ACKACT Acknowledge Action
This bit defines the master’s behavior under certain conditions defined by the bus protocol state and software interaction. The acknowledge action is performed when DATA is read, or when an execute command is written to the CMD bits.
The ACKACT bit is not a flag or strobe, but an ordinary read/write accessible register bit. The default ACKACT for master read interrupt is “Send ACK” (0). For master write, the code will know that no acknowledge should be sent since it is itself sending data.
| Value | Description |
|---|---|
| 0 | Send ACK |
| 1 | Send NACK |
Bits 1:0 – MCMD[1:0] Command
The master command bits are strobes. These bits are always read as zero.
Writing to these bits triggers a master operation as defined by the table below.
| MCMD[1:0] | DIR | Description |
|---|---|---|
| 0x0 | X | NOACT - No action |
| 0x1 | X | REPSTART - Execute Acknowledge Action succeeded by repeated Start |
| 0x2 | 0 | RECVTRANS - Execute Acknowledge Action succeeded by a byte read operation |
| 1 | Execute Acknowledge Action (no action) succeeded by a byte send operation(1) | |
| 0x3 | X | STOP - Execute Acknowledge Action succeeded by issuing a Stop condition |
- For a master being a sender, it will normally wait for new data written to the Master Data register (TWIn.MDATA).