HS401x Datasheet

R36DS0023EU0104 Rev.1.04

Mar 14, 2023

Page 10

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

4.4

Measurements and Commands

There are two types of measurement commands:

1.

Hold measurement commands: The HS401x series sensor holds the SCL line low during the measurement

and releases the SCL line when the measurement is complete. This lets the master know exactly when the

measurement has finished. Using this mode will prevent the master from communicating with any other

slave until the measurement is complete. Note that the minimum frequency for the SCL clock in this mode is

200kHz.

2.

No-hold measurement commands: The HS401x series sensor does not hold the SCL line low, and the

master is free to initiate communication with other slaves while the chip is performing the measurement. To

obtain the measurement data, the master must request the result from the chip after the expected

conversion time which depends on the measurement resolution as summarized in section 0. There is no

minimum clock frequency when in this mode.

4.4.1.

Performing a Hold Measurement

A hold measurement sequence consists of the following steps, as illustrated in Figure 9.

1.

Wake up the HS401x series sensor from sleep mode by sending its I2C address with a write bit and initiate a

measurement by sending the desired hold measurement command.

2.

Change the direction of communication by sending a start bit, the HS401x I2C address, and a read bit. The

SCL line is held low by the sensor during the measurement process, which prevents the master from

initiating any communications with other slaves on the bus.

3.

Once the requested measurement is completed by the HS401x series sensor, the SCL line is released and

the chip waits for the SCL clock signal to send the results. The sensor will then transmit the requested

measurement data on the bus for the master to capture.