Datasheet

ATmega48/88/168 Automotive [DATASHEET]
7530K–AVR–07/14
182
The TWINT flag is set in the following situations:
● After the TWI has transmitted a START/REPEATED START condition.
● After the TWI has transmitted SLA+R/W.
● After the TWI has transmitted an address byte.
● After the TWI has lost arbitration.
● After the TWI has been addressed by own slave address or general call.
● After the TWI has received a data byte.
● After a STOP or REPEATED START has been received while still addressed as a slave.
● When a bus error has occurred due to an illegal START or STOP condition.
19.6 TWI Register Description
19.6.1 TWI Bit Rate Register – TWBR
• Bits 7..0 – TWI Bit Rate Register
TWBR selects the division factor for the bit rate generator. The bit rate generator is a frequency divider which generates the
SCL clock frequency in the master modes. See Section 19.5.2 “Bit Rate Generator Unit” on page 181 for calculating bit
rates.
19.6.2 TWI Control Register – TWCR
The TWCR is used to control the operation of the TWI. It is used to enable the TWI, to initiate a master access by applying a
START condition to the bus, to generate a receiver acknowledge, to generate a stop condition, and to control halting of the
bus while the data to be written to the bus are written to the TWDR. It also indicates a write collision if data is attempted
written to TWDR while the register is inaccessible.
• Bit 7 – TWINT: TWI Interrupt Flag
This bit is set by hardware when the TWI has finished its current job and expects application software response. If the I-bit in
SREG and TWIE in TWCR are set, the MCU will jump to the TWI interrupt vector. While the TWINT flag is set, the SCL low
period is stretched. The TWINT flag must be cleared by software by writing a logic one to it. Note that this flag is not
automatically cleared by hardware when executing the interrupt routine. Also note that clearing this flag starts the operation
of the TWI, so all accesses to the TWI address register (TWAR), TWI status register (TWSR), and TWI data register (TWDR)
must be complete before clearing this flag.
• Bit 6 – TWEA: TWI Enable Acknowledge Bit
The TWEA bit controls the generation of the acknowledge pulse. If the TWEA bit is written to one, the ACK pulse is
generated on the TWI bus if the following conditions are met:
1. The device’s own slave address has been received.
2. A general call has been received, while the TWGCE bit in the TWAR is set.
3. A data byte has been received in master receiver or slave receiver mode.
Bit 76543210
TWBR7 TWBR6 TWBR5 TWBR4 TWBR3 TWBR2 TWBR1 TWBR0 TWBR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE TWCR
Read/Write R/W R/W R/W R/W R R/W R R/W
Initial Value00000000