Frame 1 Two-Wire Slave Address Byte

Frame 2 Pointer Register Byte

1

Start By

Master

ACK By

Device

ACK By

Device

Frame 3 Two-Wire Slave Address Byte

Frame 4 Data Byte 1 Read Register

Start By

Master

ACK By

Device

NACK By

Master

(2)

From

Device

1

9

1

9

1

9

1

9

SDA

SCL

0

0

1

R/W

P7

P6

P5

P4

P3

P2

P1

P0

¼

¼

¼

¼

SDA

(Continued)

SCL

(Continued)

1

0

0

1

1

0

0

(1)

1

0

0

(1)

R/W

D7

D6

D5

D4

D3

D2

D1

D0

TMP451

SBOS686A – JUNE 2013 – REVISED DECEMBER 2014

www.ti.com

Programming (continued)

(1) Slave address 1001100 shown.

(2) Master should leave SDA high to terminate a single-byte read operation.

Figure 16. Two-Wire Timing Diagram for Single-Byte Read Format

7.5.1.3 Serial Bus Address

To communicate with the TMP451 device, the master must first address slave devices using a slave address

byte. The slave address byte consists of seven address bits, and a direction bit indicating the intent of executing

a read or write operation. The TMP451 device has a device address of 4Ch (1001 100b). Additional factory-

programmed device addresses are available upon request.

7.5.1.4 Read and Write Operations

Accessing a particular register on the TMP451 device is accomplished by writing the appropriate value to the

pointer register. The value for the pointer register is the first byte transferred after the slave address byte with the

R/W bit low. Every write operation to the TMP451 device requires a value for the pointer register (see Figure 15).

When reading from the TMP451 device the last value stored in the pointer register by a write operation is used to

determine which register is read by a read operation. To change which register is read for a read operation, a

new value must be written to the pointer register. This transaction is accomplished by issuing a slave address

byte with the R/W bit low, followed by the pointer register byte; no additional data are required. 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; see Figure 16 for details of this sequence.

If repeated reads from the same register are desired, it is not necessary to continually send the pointer register

bytes, because the TMP451 device retains the pointer register value until it is changed by the next write

operation. The register bytes are sent MSB first, followed by the LSB.

Read operations should be terminated by issuing a not-acknowledge command at the end of the last byte to be

read. For single-byte operation, the master must leave the SDA line high during the acknowledge time of the first

byte that is read from the slave.

14

Submit Documentation Feedback

Copyright © 2013–2014, Texas Instruments Incorporated

Product Folder Links: TMP451