Datasheet

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EEH210

6.2. senDing a commanD

After sending the Start condition, the subsequent I

C header consists of the 7 bit I

C device address ‘1000000’ and an

SDA direction bit (Read R: ‘1’, Write W: ‘0’). The sensor indicates the proper reception of a byte by pulling the SDA pin

low (ACK bit) after the falling edge of the 8th SCL clock.

After the issue of a measurement command (‘11100011’ for temperature, ‘11100101’ for relative humidity), the MCU must

wait for the measurement to complete. The basic commands are summarized in Table 8.

COMMAND COMMENT CODE

Trigger T+RH measurement hold master 11100001

Trigger T measurement hold master 11100011

Trigger RH measurement hold master 11100101

Trigger T+RH measurement no hold master 11110001

Trigger T measurement no hold master 11110011

Trigger RH measurement no hold master 11110101

Write user register 11100110

Read user register 11100111

Soft reset 11111110

Table 10: Basic command set, RH stands for relative humidity, and T stands for temperature.

6.3. holD / no holD master moDe

There are two different operation modes to communicate with the sensor: Hold Master mode or No Hold Master mode.

In the first case the SCL line is blocked (controlled by sensor) during measurement process while in the latter case the

SCL line remains open for other communication while the sensor is processing the measurement.

No hold master mode allows for processing other I

C communication tasks on a bus while the sensor is measuring. A

communication sequence of the two modes is displayed in Figure 9 and Figure 10, respectively.

In the hold master mode, the EEH210 pulls down the SCL line while measuring to force the master into a wait state. By

releasing the SCL line the sensor indicates that internal processing is terminated and that transmission may be continued.

Figure 11: Hold master communication sequence – grey blocks are controlled by EEH210. Bit 45 may be changed to NACK followed by

Stop condition (P) to omit checksum transmission.

In no hold master mode, the MCU has to poll for the termination of the internal processing of the sensor. This is done by

sending a Start condition followed by the I

C header (10000001) as shown in Figure 10.

If the internal processing is finished, the sensor acknowledges the poll of the MCU and data can be read by the MCU. If

the measurement processing is not finished the sensor answers no ACK bit and the Start condition must be issued once

more.

For both modes, since the maximum resolution of a measurement is 14 bit, the two last least significant bits (LSBs, bits

43 and 44) are used for transmitting status information. Bit 1 of the two LSBs indicates the measurement type (‘0’:tem-

perature, ‘1’:humidity). Bit 0 is currently not assigned.