37.6.2.4 I2C Host Operation
The I2C host is byte-oriented and interrupt based. The number of interrupts generated is kept at a minimum by automatic handling of most incidents. The software driver complexity and code size are reduced by auto-triggering of operations, and a Special Smart mode, which can be enabled by the Smart Mode Enable bit in the Control B register (CTRLB.SMEN).
The I2C host has two interrupt strategies.
When SCL Clock Stretch Mode (CTRLA.SCLSM) is '0', SCL is stretched before or after the Acknowledge bit . In this mode the I2C host operates according to the following figure. The circles labeled "Mn" (M1, M2..) indicate the nodes the bus logic can jump to, based on software or hardware interaction.
This diagram is used as reference for the description of the I2C host operation throughout the document.
In the second strategy (CTRLA.SCLSM=1), interrupts only occur after the ACK bit, as shown in the following figure. This strategy can be used when it is not necessary to check DATA before acknowledging.
