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4.10 Reset

A system reset of the SHT85 can be generated externally by issuing a command (soft reset). Additionally, a system reset

is generated internally during power-up. During the reset procedure the sensor will not process commands.

Interface Reset

If communication with the device is lost, the following signal sequence will reset the serial interface: While leaving SDA

high, toggle SCL nine or more times. This must be followed by a Transmission Start sequence preceding the next

command. This sequence resets the interface only. The status register preserves its content.

Soft Reset / Re-Initialization

The SHT85 provides a soft reset mechanism that forces the system into a well-defined state without removing the power

supply. When the system is in idle state the soft reset command can be sent to the SHT85. This triggers the sensor to

reset its system controller and reloads calibration data from the memory. In order to start the soft reset procedure the

command as shown in Table 13 should be sent.

It is worth noting that the sensor reloads calibration data prior to every measurement by default.

Command

Hex Code

Soft Reset

0x30A2

Table 13: Soft reset command (Clear blocks are controlled by

the microcontroller, grey blocks by the sensor).

Reset through General Call

Additionally, a reset of the sensor can also be generated using the “general call” mode according to I2C-bus

specification15. It is important to understand that a reset generated in this way is not device specific. All devices on the

same I2C bus that support the general call mode will perform a reset. Additionally, this command only works when the

sensor is able to process I2C commands. The appropriate command consists of two bytes and is shown in Table 14.

Command

Code

Address byte

0x00

Second byte

0x06

Reset command using the

general call address

0x0006

Table 14: Reset through the general call address (Clear blocks

are controlled by the microcontroller, grey blocks by the

sensor).

Hard Reset

A hard reset is achieved by switching the supply voltage to the VDD Pin off and then on again. In order to prevent

powering the sensor over the ESD diodes, the voltage to pins 1 (SCL) and 4 (SDA) also needs to be removed.

S General Call Address

1

2

3

4

5

6

7

8

9

Reset Command

1

2

3

4

5

6

7

8

9