Datasheet

23.9.2. TWI Status Register
Name: TWSR
Offset: 0xB9
Reset: 0xF8
Property: -
Bit 7 6 5 4 3 2 1 0
TWS7 TWS6 TWS5 TWS4 TWS3 TWPS[1:0]
Access
R R R R R R R/W R/W
Reset 1 1 1 1 1 0 0 0
Bits 3, 4, 5, 6, 7 – TWS3, TWS4, TWS5, TWS6, TWS7: TWI Status Bit
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 – TWPS[1:0]: TWI Prescaler
These bits can be read and written, and control the bit rate prescaler.
Table 23-8. TWI Bit Rate Prescaler
TWS[1:0] Prescaler Value
00 1
01 4
10 16
11 64
To calculate bit rates, refer to Bit Rate Generator Unit. The value of TWPS1...0 is used in the equation.
Atmel ATmega644A [DATASHEET]
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