ATH25 Data Sheet

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Version:V1.0 —— May 2021

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Figure 11. Stop transmission state (P)

When SCL is high, the SDA line changes from low to high. The stop state is a special bus state

controlled by the master, indicating the end of the slave transmission (after Stop, the BUS is

generally considered to be in an idle state).

7.3 Send Command

After the transmission is started, the first byte of the I2C transmitted subsequently includes the

7-bit I2C device address 0x38 and an SDA direction bit x (read R: ‘1’, write W: ‘0’). After

the 8th falling edge of the SCL clock, pull down the SDA pin (ACK bit) to indicate that the

sensor data is received normally. After sending the initialization command (‘1110’0001’

represents initialization, ‘1010’1100’ represents temperature and humidity measurement),

the MCU must wait until the measurement is completed. The basic commands are

summarized in Table 9 and Table 10 shows the status bit description returned by the slave.

Command

Code

Initialization

Command

1110‘001

Trigger

Measurement

1010’1100

Soft Reset

1011‘1010

Table 9. Basic Command Set

Bits

Significance

Description

Bit[7]

Busy indication

1-Equipment is busy, in measurement

mode

0- Equipment is idle, in hibernation state

Bit[6:5]

Retain

Retain

Bit[4]

Retain

Retain

Bit[3]

CAL Enable

1 - Calibrated

0 - Uncalibrated

Bit[2:0]

Retain

Retain

Table 10. Status bit description

7.4 Sensor Reading Process

1.After power-on, wait no less than 100ms. Before reading the temperature and humidity value,

get a byte of status word by sending 0x71. If the status word and 0x18 are not equal to 0x18,

initialize the 0x1B, 0x1C, 0x1E registers, details Please refer to our official website routine for

the initialization process; if they are equal, proceed to the next step.

2.Wait 10ms to send the 0xAC command (trigger measurement). This command parameter

has two bytes, the first byte is 0x33, and the second byte is 0x00.

3.Wait 80ms for the measurement to be completed, if the read status word Bit [7] is 0, it means

the measurement is completed, and then six bytes can be read continuously; otherwise,