www.sensirion.com

Version 3 – August 2020

9/23

4 Operation and Communication

The SHT85 supports I2C fast mode (and frequencies up to 1000 kHz). For detailed information on the I2C protocol, refer

After sending a command to the sensor a minimal waiting time of 1ms is needed before another command can

be received by the sensor.

Furthermore, to keep self-heating below 0.1°C, SHT85 should not be active for more than 10% of the time.

All SHT85 commands and data are mapped to a 16-bit address space. Additionally, data and commands are protected

with a CRC checksum. This increases communication reliability. The 16 bits commands to the sensor already include a

3 bit CRC checksum. Data sent from and received by the sensor is always succeeded by an 8 bit CRC.

In write direction it is mandatory to transmit the checksum, since the SHT85 only accepts data if it is followed by the

correct checksum. In read direction it is left to the master to read and process the checksum.

4.1 I2C Address

The I2C device address is given in

Table 7: SHTC85 I2C device address.

SHT85

Hex. Code

Bin. Code

0x44

100’0100

4.2 Power-Up and Communication Start

commands from the master (microcontroller).

Each transmission sequence begins with a START condition (S) and ends with a STOP condition (P) as described in the

I2C-bus specification. Whenever the sensor is powered up, but not performing a measurement or communicating, it

automatically enters idle state for energy saving. This idle state cannot be controlled by the user.

4.3 Starting a Measurement

A measurement communication sequence consists of a START condition, the I2C write header (7-bit I2C device address

plus 0 as the write bit) and a 16-bit measurement command. The proper reception of each byte is indicated by the sensor.

It pulls the SDA pin low (ACK bit) after the falling edge of the 8th SCL clock to indicate the reception. A complete

measurement cycle is depicted in Table 8.

With the acknowledgement of the measurement command, the SHT85 starts measuring humidity and temperature.

4.4 Measurement Commands for Single Shot Data Acquisition Mode

In this mode one issued measurement command triggers the acquisition of one data pair. Each data pair consists of one

16-bit temperature and one 16-bit humidity value (in this order). During transmission each data value is always followed

by a CRC checksum, see Section 4.5.

In single shot mode different measurement commands can be selected. The 16-bit commands are shown in Table 8.

They differ with respect to repeatability (low, medium and high).

15 http://www.nxp.com/documents/user_manual/UM10204.pdf