ATSHA204A datasheet(28/93 Pages) MICROCHIP

28 / 93 page

I2C Interface

The I2C interface uses the SDA and SCL pins to indicate various I/O states to the ATSHA204A. This

interface is designed to be compatible at the protocol level with other I2C devices operating up to 1 MHz.

The SDA pin must be pulled high with an external pull-up resistor, as the ATSHA204A includes only an

open-drain driver on its output pin. The bus master may be either open-drain or totem pole and if the

latter, then it should be tri-stated when the ATSHA204A is driving results on the bus. The SCL pin is an

input and must be driven both high and low at all times by an external device or pull-up.

6.1

I/O Conditions

The ATSHA204A device responds to the following I/O conditions outlined in the Device is Asleep and

Device is Awake sections.

6.1.1

Device is Asleep

When the device is asleep, it ignores all but the Wake condition.

•

Wake: If SDA is held low for a period greater than tWLO, the device exits low-power mode and, after

a delay of tWHI, is ready to receive I2C commands. The device ignores any levels or transitions on

the SCL pin when the device is idle or asleep and during tWLO. At some point during tWHI, the SCL

pin is enabled and the conditions listed in Section Device is Awake, are honored.

The Wake condition requires that either the system processor manually drives the SDA pin low for tWLO,

or that a data byte of 0x00 is transmitted at a clock rate sufficiently slow so that SDA is low for a

minimum period of tWLO. When the device is awake, the normal processor I2C hardware and/or software

can be used for device communications up to and including the I/O sequence required to put the device

back into low-power (for example sleep) mode.

When there are multiple ATSHA204A devices on the bus and the I2C interface is run at 133 KHz or

slower, the transmission of certain data patterns (such as 0x00) causes all the ATSHA204A devices on

the bus to wake-up. Because subsequent device addresses transmitted along the bus can only match the

desired devices, the unused devices remain inactive and do not cause any bus conflicts.

In I2C mode, the device ignores a wake sequence that is sent when the device is already awake.

6.1.2

Device is Awake

When the device is awake, it honors the conditions listed below:

•

Data Zero: if SDA is low and stable while SCL goes from low to high to low, then a zero bit is being

transferred on the bus. SDA can change while SCL is low.

•

Data One: if SDA is high and stable while SCL goes from low to high to low, then a one bit is being

transferred on the bus. SDA can change while SCL is low.

ATSHA204A

I2C Interface

DS40002025A-page 28

ATSHA204A датащи(PDF) 28 Page - Microchip Technology