and write operations as the command execution is dependent on the STATUS.DIR bit. Writing ‘1’ to
INTFLAG.AMATCH will also cause an ACK/NACK to be sent corresponding to the CTRLB.ACKACT bit.
Case 2: Address packet accepted – Write flag set
The STATUS.DIR bit is cleared, indicating an I
2
C master write operation. The SCL line is forced low,
stretching the bus clock. If an ACK is sent, the I
2
C slave will wait for data to be received. Data, repeated
start or stop can be received.
If a NACK is sent, the I
2
C slave will wait for a new start condition and address match. Typically, software
will immediately acknowledge the address packet by sending an ACK/NACK. The I
2
C slave command
CTRLB.CMD = 3 can be used for both read and write operation as the command execution is dependent
on STATUS.DIR.
Writing ‘1’ to INTFLAG.AMATCH will also cause an ACK/NACK to be sent corresponding to the
CTRLB.ACKACT bit.
Receiving Address Packets (SCLSM=1)
When SCLSM=1, the I
2
C slave will stretch the SCL line only after an ACK, see
. When the I
2
C slave is properly configured, it will wait for a start condition to be detected.
When a start condition is detected, the successive address packet will be received and checked by the
address match logic.
If the received address is not a match, the packet will be rejected and the I
2
C slave will wait for a new
start condition.
If the address matches, the acknowledge action as configured by the Acknowledge Action bit Control B
register (CTRLB.ACKACT) will be sent and the Address Match bit in the Interrupt Flag register
(INTFLAG.AMATCH) is set. SCL will be stretched until the I
2
C slave clears INTFLAG.AMATCH. As the
I
2
C slave holds the clock by forcing SCL low, the software is given unlimited time to respond to the
address.
The direction of a transaction is determined by reading the Read/Write Direction bit in the Status register
(STATUS.DIR). This bit will be updated only when a valid address packet is received.
If the Transmit Collision bit in the Status register (STATUS.COLL) is set, the last packet addressed to the
I
2
C slave had a packet collision. A collision causes the SDA and SCL lines to be released without any
notification to software. The next AMATCH interrupt is, therefore, the first indication of the previous
packet’s collision. Collisions are intended to follow the SMBus Address Resolution Protocol (
ARP
).
After the address packet has been received from the I
2
C master, INTFLAG.AMATCH be set to ‘1’ to clear
it.
Receiving and Transmitting Data Packets
After the I
2
C slave has received an address packet, it will respond according to the direction either by
waiting for the data packet to be received or by starting to send a data packet by writing to DATA.DATA.
When a data packet is received or sent, INTFLAG.DRDY will be set. After receiving data, the I
2
C slave
will send an acknowledge according to CTRLB.ACKACT.
Case 1: Data received
INTFLAG.DRDY is set, and SCL is held low, pending for SW interaction.
Case 2: Data sent
When a byte transmission is successfully completed, the INTFLAG.DRDY interrupt flag is set. If NACK is
received, indicated by STATUS.RXNACK=1, the I
2
C slave must expect a stop or a repeated start to be
received. The I
2
C slave must release the data line to allow the I
2
C master to generate a stop or repeated
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
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