5.1.3

READ byte

The READ byte protocol is used to read one byte of data from the registers as shown in the following table.

Start

Slave

address

WR

ACK

Register

address

ACK

start

Slave

address

RD

ACK

data

NACK

stop

1 bit

7 bits

1 bit

1 bit

8 bits

1 bit

8 bits

1 bit

1 bit

5.1.4

SEND byte

The SEND byte protocol is used to set the internal address register to the correct address. It sends a register

address with no data (see following table). The SEND byte can be followed by the RECEIVE byte protocol

described in the following section in order to read data from the register

Start

Slave

address

WR

ACK

Register

address

ACK

stop

1 bit

7 bits

1 bit

1 bit

8 bits

1 bit

1 bit

5.1.5

RECEIVE byte

The RECEIVE byte protocol is used to read data from the register when the internal register address pointer is

known (see following table). This can be used for consecutive reads of the same register.

Start

Slave

address

RD

ACK

data

NACK

stop

1 bit

7 bits

1 bit

1 bit

8 bits

1 bit

1 bit

5.1.6

SMBus timeout

The STTS22H supports SMBus timeout which is enabled by default at power-up. This can be disabled via bit 1 in

the CTRL register. When timeout is enabled, the STTS22H will time out after 30 ms (typ) of inactivity. The

STTS22H resets and releases the bus. This feature is turned on by default.

5.1.7

Alert response address

The STTS22H supports the SMBus alert response address (ARA) protocol. In the event of an out-of-limit

temperature measurement, the ALERT / INT output will be asserted. In response, the host (supporting the ARA

protocol) will send the SMBus Alert Response Address to the general (slave) address of 0001_100b. All devices

with active interrupts will respond with their client addresses (with the LSB bit set to 0). The STTS22H will

acknowledge the ARA and respond with its slave device address. ARA transfer details are available in the

following table.

Start

Alert response

address

RD

ACK

STTS22H slave

address

NACK

Stop

1 bit

7 bit

1 bit

1 bit

8 bit

1 bit

1 bit

STTS22H

SMBus interface

DS12606 - Rev 4

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