XMEGAA Datasheet, PDF (199/375 Pages) ATMEL Corporation – 8-bit XMEGAA Microcontroller

XMEGA A
• Bit 7:3 - Res: Reserved
These bits are unused and reserved for future use. For compatibility with future devices, always
write these bits to zero when this register is written.
• Bit 2 - ACKACT: Acknowledge Action
The Acknowledge Action (ACKACT) bit defines the slave's acknowledge behavior after an
address or data byte is received from the master. The Acknowledge Action is executed when a
command is written to the CMD bits. If the SMEN bit in the CTRLA register is set, the Acknowl-
edge Action is performed when the DATA register is read.
Table 17-6 lists the acknowledge actions.
Table 17-6. TWI slave acknowledge action
ACKACT
Action
0
Send ACK
1
Send NACK
• Bit 1:0 - CMD[1:0]: Command
Writing the Command (CMD) bits triggers the slave operation as defined by Table 17-7. The
CMD bits are strobe bits, and always read as zero. The operation is dependent on the slave
interrupt flags, DIF and APIF. The Acknowledge Action is only executed when the slave receives
data bytes or address byte from the master.
Table 17-7. TWI slave command
CMD[1:0]
DIR
Operation
00
X
No action
01
X
Reserved
Used to complete transaction
10
0
Execute Acknowledge Action succeeded by waiting for any START
(S/Sr) condition.
1
Wait for any START (S/Sr) condition.
Used in response to an Address Byte (APIF is set)
0
Execute Acknowledge Action succeeded by reception of next byte.
1
Execute Acknowledge Action succeeded by the DIF being set
11
Used in response to a Data Byte (DIF is set)
0
Execute Acknowledge Action succeeded by waiting for the next byte.
1
No operation.
Writing the CMD bits will automatically clear the slave interrupt flags, the CLKHOLD flag and
release the SCL line. The ACKACT bit and CMD bits can be written at the same time, and then
the Acknowledge Action will be updated before the command is triggered.
8077B–AVR–06/08
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