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HDC1000

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SNAS643C – JULY 2014 – REVISED JANUARY 2016

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8.5 Programming

8.5.1 I2C Serial Bus Address Configuration

To communicate with the HDC1000, 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 HDC1000 features two address pins to allow up to 4 devices to be addressed on a single

bus. Table 1 describes the pin logic levels used to properly connect up to 4 devices. The state of the ADR0 and

ADR1 pins is sampled on every bus communication and should be set before any activity on the interface

occurs. The address pin is read at the start of each communication event.

Table 1. HDC1000 ADDRESS

ADR1

ADR0

ADDRESS (7-bit address)

0

0

1000000

0

1

1000001

1

0

1000010

1

1

1000011

8.5.2 I2C Interface

The HDC1000 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 HDC1000 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.

8.5.2.1 Serial Bus Address

To communicate with the HDC1000, 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.

8.5.2.2 Read and Write Operations

Access a particular register on the HDC1000 by writing the appropriate 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

HDC1000 requires a value for the pointer register (refer to Figure 10).

When reading from the HDC1000, the last value stored in the pointer by a write operation is used to determine

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

be written to the pointer. 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.