ATSHA204A datasheet(29/93 Pages) MICROCHIP

29 / 93 page

Figure 6-1. Data Bit Transfer on I2C Interface

SCL

Data Line

Stable;

Data Valid

Change

of Data

Allowed

SDA

•

Start Condition: a high-to-low transition of SDA with SCL high is a Start condition, which must

precede all commands.

•

Stop Condition: a low-to-high transition of SDA with SCL high is a Stop condition. After this

condition is received by the device, the current I/O transaction ends. On input, if the device has

sufficient bytes to execute a command, the device transitions to the busy state and begins

execution. Microchip recommends that a Stop condition be sent after any packet is sent to the

device although it may not always be required. The device starts when the correct number of bytes

is received. In the case of an error on the bus, the device resets on the watchdog timer.

Figure 6-2. Start and Stop Conditions on I2C Interface

SCL

SDA

Start

Condition

Stop

Condition

•

Acknowledge (ACK): on the ninth clock cycle after every address or data byte has been

transferred, the receiver pulls the SDA pin low to acknowledge proper reception of the byte.

•

Not Acknowledge (NACK): alternatively, on the ninth clock cycle after every address or data byte

has been transferred, the receiver can leave the SDA pin high to indicate that there was a problem

with the reception of the byte or that this byte completes the block transfer.

ATSHA204A

I2C Interface

DS40002025A-page 29

ATSHA204A Datasheet(PDF) 29 Page - Microchip Technology