Rainbow Electronics ATmega128RFA1 - Manual (Page 403)

403
8266A-MCU Wireless-12/09
ATmega128RFA1
pins enabling the slew-rate limiters and spike filters. If this bit is written to zero, the TWI
is switched off and all TWI transmissions are terminated regardless of any ongoing
operation.
• Bit 1 – Res - Reserved Bit
This bit is reserved for future use. A read access always will return zero. A write access
does not modify the content.
• Bit 0 – TWIE - TWI Interrupt Enable
When this bit is written to one and the I-bit in SREG is set, the TWI interrupt request will
be activated for as long as the TWINT Flag is high.
25.9.3 TWSR – TWI Status Register
Bit 7 6 5 4 3 2 1 0
NA ($B9) TWS7 TWS6 TWS5 TWS4 TWS3 Res TWPS1 TWPS0 TWSR
Read/Write RW RW RW RW RW R RW RW
Initial Value 0 0 0 0 0 0 0 0
• Bit 7:3 – TWS4:0 - TWI Status
These 5 bits reflect the status of the TWI logic and the 2-wire Serial Bus. The different
status codes for both transmitter and receiver mode are described in the following table.
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.
Table 25-8 TWS Register Bits
Register Bits Value Description
0x00 Bus error due to illegal START or STOP
condition.
0x08 A START condition has been transmitted.
0x10 A repeated START condition has been
transmitted.
0x18 SLA+W has been transmitted; ACK has
been received.
0x20 SLA+W has been transmitted; NOT ACK has
been received.
0x28 Data byte has been transmitted; ACK has
been received.
0x30 Data byte has been transmitted; NOT ACK
has been received.
0x38 Arbitration lost in SLA+W or data bytes
(Transmitter); Arbitration lost in SLA+R or
NOT ACK bit (Receiver).
0x40 SLA+R has been transmitted; ACK has been
received.
0x48 SLA+R has been transmitted; NOT ACK has
been received.
TWS4:0
0x50 Data byte has been received; ACK has been