HS401x Datasheet

R36DS0023EU0103 Rev.1.03

Jun 6, 2022

Page 10

Figure 13. START and STOP Condition Waveform

After the START bit, the master device sends the 7-bit slave address (see section 4.2) to the HS401x, followed

by the read/write bit, which indicates the transfer direction of any subsequent data. This bit is set to 1 to indicate

a read from slave to master or set to 0 to indicate a write from master to slave.

All transfers consist of 8 bits and a response bit: 0 for Acknowledge (ACK) or 1 for Not Acknowledge (NACK).

After the ACK is received, another data byte can be transferred or the communication can be stopped with a

STOP bit.

The HS401x series sensors are equipped with different commands to configure the chip and to perform

measurement as described in Table 4.

Table 4. Commands Code and Description

Command Code (HEX)

Description

0xE3

Hold Temperature Measurement

0xF3

No-hold Temperature Measurement

0xE5

Hold Humidity and Temperature Measurement

0xF5

No-hold Humidity and Temperature Measurement

0xA7

Read Register

0xA6

Write Register

0x30

Stop Periodic Measurements

0xD7

Read Sensor ID

The Hold and No-hold commands will be described in section 4.4, and the read and write register commands will

be described in section 4.7. The HS401x sensor can measure only temperature or both humidity and

temperature as described in Table 8. Both options return fully calibrated measurements that can be converted to

humidity and temperature readings using the equations in section 4.4.3.

Table 5. Measurement Command Modes

Measurement

Command Mode

Description

Number of data bytes

sent on the I2C bus

Temperature

The chip only measures temperature and sends the 14-bit result once the

measurement is complete.

2 bytes + 1 byte CRC

Humidity and

Temperature

The chip measures humidity and temperature and sends the 14-bit humidity

result followed by the 14-bit temperature result once the measurement is

complete.

4 bytes + 1 byte CRC

START Condition

STOP Condition

STOP

SDA

SCL

SDA

SCL

START