219
XMEGA A [MANUAL]
8077I–AVR–11/2012
this is prevented by hardware. The DATA register can only be accessed when the SCL line is held low by the master; i.e.,
when CLKHOLD is set.
In master write mode, writing the DATA register will trigger a data byte transfer followed by the master receiving the
acknowledge bit from the slave. WIF and CLKHOLD are set.
In master read mode, RIF and CLKHOLD are set when one byte is received in the DATA register. If smart mode is
enabled, reading the DATA register will trigger the bus operation as set by the ACKACT bit. If a bus error occurs during
reception, WIF and BUSERR are set instead of RIF.
Accessing the DATA register will clear the master interrupt flags and CLKHOLD.
19.10 Register Description – TWI Slave
19.10.1 CTRLA
Control register A
Bit 7:6
INTLVL[1:0]: Interrupt Level
These bits select the interrupt level for the TWI master interrupt, as described in “Interrupts and Programmable Multilevel
Bit 5
DIEN: Data Interrupt Enable
Setting the data interrupt enable (DIEN) bit enables the data interrupt when the data interrupt flag (DIF) in the STATUS
register is set. The INTLVL bits must be nonzero for the interrupt to be generated.
Bit 4
APIEN: Address/Stop Interrupt Enable
Setting the address/stop interrupt enable (APIEN) bit enables the address/stop interrupt when the address/stop interrupt
flag (APIF) in the STATUS register is set. The INTLVL bits must be nonzero for interrupt to be generated.
Bit 3
ENABLE: Enable TWI Slave
Setting this bit enables the TWI slave.
Bit 2
PIEN: Stop Interrupt Enable
Setting the this bit will cause APIF in the STATUS register to be set when a STOP condition is detected.
Bit 1
PMEN: Promiscuous Mode Enable
By setting this bit, the slave address match logic responds to all received addresses. If this bit is cleared, the address
match logic uses the ADDR register to determine which address to recognize as its own address.
Bit 0
SMEN: Smart Mode Enable
This bit enables smart mode. When Smart mode is enabled, the acknowledge action, as set by the ACKACT bit in the
CTRLB register, is sent immediately after reading the DATA register.
19.10.2 CTRLB
Control register B
Bit 7:3
Reserved
Bit
7
6
5432
1
0
+0x00
INTLVL[1:0]
DIEN
APIEN
ENABLE
PIEN
PMEN
SMEN
Read/Write
R/W
Initial Value
0
0000
0
Bit
76543210
+0x01
ACKACT
CMD[1:0]
Read/Write
RRRRR
R/W
Initial Value
00000000
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