Figure 13 Start Transfer Status ( S ) - When SCL is high, SDA transitions from high

to low. The start state is a special bus state controlled by the host, indicating the

start of the slave transfer ( after the Start , the BUS bus is generally considered

to be busy)

Figure 14 Stop Transfer Status ( P ) - When SCL is high, the SDA line transitions

from low to high. The stop state is a special bus state controlled by the master

that indicates the end of the slave transfer ( after the Stop , the BUS bus is

generally considered to be idle).

5.3 send command

After the transmission is initiated, the subsequently

transmitted I 2 C first byte includes the 7 -bit I 2 C

device address 0x38 and one SDA direction (read R :

'1' , write W : '0' ). After the first falling edge of the

SCL clock 8, by pulling the SDA pin (ACK bit),

indicating proper reception of the sensor. After

issuing the initialization command ( '1110'0001'

represents initialization, '1010'1100' stands for

temperature and humidity measurement), the MCU

must wait for the measurement to be completed. The

basic commands are summarized in Table 9 . Table 10

shows the status bit descriptions returned by the

slave.

command

Interpretation

Code

Initialization

command

Keep the host

1110’0001

Trigger

measurement

Keep the host

1010’1100

Soft reset

1011’1010

Table 9 basic command set

Bit

significance

description

Bit[7]

Busy indication

1 --

0 --

The device is busy，

the device is in the

measurement state, and the

device is idle.

Bit[6:5]

Current working mode

(Mode Status)

00

01

1x

Currently NOR

Currently CYC

Currently CMD

mode

mode

mode

Bit[4]

Reserved

Reserved

Bit[3]

Calibration enable

bit

CAL Enable

1-calibrated

0-- not calibrated

Bit[2：0]

Reserved

Reserved

Table 10 status bit description

Trigger measurement data

ACK

S

Start

P Stop

Note: The sensor takes time to collect . After the host sends a

measurement command ( 0xAC ) , the delay is over 75ms and the

converted data is read and the returned status bit is normal. If the

status bit [Bit7 of] is 0 for the data can be read normally, the sensor 1

is the busy state, the host needs to wait for the data processing is

completed.

5.4 Soft reset

This command (see Table 9 ) is used to restart the

sensor system without turning the power off and on

again. After receiving this command, the sensor

system begins to reinitialize and restores the default

settings. The soft reset takes less than 20ms

S 0 1 1 1 0 0 0 0

1 0 1 0 1 1 0 0

I2C address +write

Trigger

measurement

0xac

00110011

00000000

P

DATA0

DATA1

读取温湿度数据

S

x

x

x

x

I2C address +read

状态

x x x x x x x x

x x x x x x x x

Humidity data

Humidity

data

x x x x x x x x

x x x x x x x x

Humidity

dataTemperature data

Temperature

data

Temperatur

e

主机到从机

从机到主机