25.8.3 TWSR – TWI Status Register
When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to these offset addresses.
| Name: | TWSR |
| Offset: | 0x01 |
| Reset: | 0xF8 |
| Property: | When addressing I/O Registers as data space the offset address is 0x21 |
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
| TWSn[4:0] | TWPSn[1:0] | ||||||||
| Access | R | R | R | R | R | R/W | R/W | ||
| Reset | 0 | 0 | 0 | 0 | 1 | 0 | 0 | ||
Bits 7:3 – TWSn[4:0] TWI Status Bit 7 [n = 7:3]
The TWS[7:3] reflect the status of the TWI logic and the 2-wire Serial Bus. The different status codes are described later in this section. Note that the value read from TWSR contains both the 5-bit status value and the 2-bit prescaler value. The application designer should mask the prescaler bits to zero when checking the Status bits. This makes status checking independent of prescaler setting. This approach is used in this datasheet, unless otherwise noted.
Bits 1:0 – TWPSn[1:0] TWI Prescaler [n = 1:0]
These bits can be read and written, and control the bit rate prescaler.
| TWPS1 | TWPS0 | Prescaler Value |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 4 |
| 1 | 0 | 16 |
| 1 | 1 | 64 |
To calculate bit rates, refer to Bit Rate Generator Unit. The value of TWPS1:0 is used in the equation.