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XMEGA A [MANUAL]
8077I–AVR–11/2012
19.6.1.4 Case S4: STOP condition received.
When the STOP condition is received, the slave address/stop flag will be set, indicating that a STOP condition, and not
an address match, occurred.
19.6.2 Receiving Data Packets
The slave will know when an address packet with R/W direction bit cleared has been successfully received. After
acknowledging this, the slave must be ready to receive data. When a data packet is received, the data interrupt flag is set
and the slave must indicate ACK or NACK. After indicating a NACK, the slave must expect a STOP or repeated START
condition.
19.6.3 Transmitting Data Packets
The slave will know when an address packet with R/W direction bit set has been successfully received. It can then start
sending data by writing to the slave data register. When a data packet transmission is completed, the data interrupt flag
is set. If the master indicates NACK, the slave must stop transmitting data and expect a STOP or repeated START
condition.
19.7
Enabling External Driver Interface
An external driver interface can be enabled. When this is done, the internal TWI drivers with input filtering and slew rate
control are bypassed. The normal I/O pin function is used, and the direction must be configured by the user software.
When this mode is enabled, an external TWI compliant tri-state driver is needed for connecting to a TWI bus.
By default, port pins 0 (Pn0) and 1 (Pn1) are used for SDA and SCL. The external driver interface uses port pins 0 to 3 for
the SDA_IN, SCL_IN, SDA_OUT, and SCL_OUT signals.