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Version:V1.0 —— May 2021

AHT20 Data Sheet

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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 bus is generally considered to be

in an idle state).

7.3 Send Command

After the transmission is started, the first byte of I²C that is subsequently transmitted includes the 7-bit I²C device

address 0x38 and a 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 measurement

command 0xAC, the MCU must wait until the measurement is completed.

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 9. Status bit description

7.4 Sensor Reading Process

1. After power-on, wait for ≥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, continue to wait.

4. After receiving six bytes, the next byte is CRC check data, which the user can read as needed. If the receiver

needs CRC check, it will send an ACK reply after receiving the sixth byte, otherwise it will send a NACK reply. The

initial value of CRC is 0xFF, and the CRC8 check polynomial is:

CRC [7:0] = 1+X4+X5+X8

5. Calculate the temperature and humidity value

Note: The calibration status check in the first step only needs to be checked when the power is turned on.No

operation is required during the acquisition process.