1

9

Ack by

Slave

Start by

Master

SCL

SDA

Frame 1

7-bit Serial Bus Address Byte

R/W

A2

A0

A1

A3

A4

A5

A6

D7

D6

D5

D4

D3

D2

D1

D0

1

9

Ack by

Slave

Stop by

Master

1

9

D15

D14

D13

D12

D11

D10

D9

D8

Ack by

Slave

Frame 3

Data MSB from

MASTER

Frame 4

Data LSB from

MASTER

1

9

P7

P6

P5

P4

P3

P2

P1

P0

Ack by

Slave

Frame 2

Pointer Register Byte

SCL

SDA

HDC1050

SNAS658C – MAY 2015 – REVISED DECEMBER 2015

www.ti.com

8.5 Programming

8.5.1 I2C Interface

The HDC1050 operates only as a slave device on the I2C bus interface. It is not allowed to have on the I2C bus

multiple devices with the same address. Connection to the bus is made via the open-drain I/O lines, SDA, and

SCL. The SDA and SCL pins feature integrated spike-suppression filters and Schmitt triggers to minimize the

effects of input spikes and bus noise. After power-up, the sensor needs at most 15 ms, to be ready to start RH

and temperature measurement. During this power-up time the HDC1050 is only able to provide the content of the

serial number registers (0xFB to 0xFF) if requested. After the power-up the sensor is in the sleep mode until a

communication or measurement is performed. All data bytes are transmitted MSB first.

8.5.1.1 Serial Bus Address

To communicate with the HDC1050, the master must first address slave devices via a slave address byte. The

slave address byte consists of seven address bits, and a direction bit that indicates the intent to execute a read

or write operation. The I2C address of the HDC1050 is 1000000 (7-bit address).

8.5.1.2 Read and Write Operations

To access a particular register on the HDC1050, write the desired register address value to the Pointer Register.

The pointer value is the first byte transferred after the slave address byte with the R/W bit low. Every write

operation to the HDC1050 requires a value for the pointer register (refer to Figure 10).

When reading from the HDC1050, the last value stored in the pointer by a write operation is used to determine

which register is accessed by a read operation. To change the pointer register for a read operation, a new value

must be written to the pointer register. This transaction is accomplished by issuing the slave address byte with

the R/W bit low, followed by the pointer byte. No additional data is required (refer to Figure 11).

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. Note that register bytes are sent MSB first, followed by the LSB. A write operation in

a read-only register such as (DEVICE ID, MANUFACTURER ID, SERIAL ID) returns a NACK after each data

byte; read/write operation to unused address returns a NACK after the pointer; a read/write operation with

incorrect I2C address returns a NACK after the I2C address.

Figure 10. Writing Frame (Configuration Register)

10

Submit Documentation Feedback

Copyright © 2015, Texas Instruments Incorporated

Product Folder Links: HDC1050