Figure 6. Two-wire Read Command Timing Diagram

When writing data to the TMP112A , after the slave address byte is sent, accessing a particular

register on the TMP112A is accomplished by writing the appropriate value to the pointer register. Every write

operation to the TMP112A requires a value for the pointer register.

When reading from the TMP112A

device, after the slave address byte is sent, the corresponding

pointer register byte also needs to be sent. Unlike the write operation, if the user need to repeatedly read data from

the same register, it is not required to send the pointer register byte separately each time, the last value stored in

the pointer register will be read by the device automatically; to change the register pointer for a read operation, a

new value must be written to the pointer register. The action is accomplished by issuing a slave-address byte

with the R/W bit low, followed by the pointer register byte. The master can then generate a START condition and

send the slave address byte with the R/W bit high to initiate the read command.

Register bytes are sent with the MSB first, followed by the LSB. Figure 5 and Figure 6 show schematic diagrams

of the above read and write operations.

SMBus Alert Function

The TMP112A supports the SMBus alert function. When the TMP112A operates in interrupt mode (TM=1), the mas-

ter can send out and SMBus ALERT command (19h) to the bus. If the ALERT pin is active, the device acknowled-

ges the SMBus ALERT command and responds by returning the slave address. The eighth bit (LSB) of the slave add-

ress byte indicates if the alert condition is caused by the temperature exceeding THIGH or falling below TLOW. This

bit is equal to POL if the temperature is greater than or equal to THIGH; this bit is equal to POL if the temperature is

less than TLOW.

If multiple devices on the bus respond to the SMBus ALERT command, the bus will return the lowest two-wire

address. The TMP112A ALERT pin becomes inactive at the completion of the SMBus ALERT command; the

ALERT pin of the TMP112A that does not return an address will remain active. Sending the SMBus ALERT com-

mand again can continue to clear the ALERT pin of the TMP112A with the current lowest address. The

above process is detailed in Figure 7.

D7

D6

D5

D4

ACK by

Master

Frame 5 Data-Byte 2 Read Register

1

9

D3

D2

D1

D0

STOP By

Master

SCL

(Continued)

SDA

(Continued)

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