- 17 -

Figure14: I

C sensors read the complete example of fig

◎I C read and write timing decomposition

Sensors read or write, you must follow these three steps, otherwise it will not communicate or

can’t read the correct data:

Step one: Wake Sensor

In order to reduce the humidity sensor errors caused by self-heating, the sensor in a

non-working state, dormant, so to read the sensor must wake sensor to transmit commands to read

and write, otherwise the sensor will not respond. It should be noted that, in the wake sensor, I C

address is sent, the sensor does not respond to ACK, but the host must send back an ACK clock

verify that the ninth SCL clock signal. Wake sensor operation is following instructions:

After the host sends a start signal is applied to the starting address, wait for sometime (waiting

time of at least 800 μs, the maximum 3ms; such as host hardware I C, you do not need to wait for

the hardware I C will automatically wait), and then sends a stop signal.

Namely: the starting signal +0 xB8 + wait (> 800us) + stop signal timing diagram shown in

Figure 15.

Figure 15: Wake Sensor

Step two : Send the read command or send written instructions

After the wake AM2321 sensors, can be fully in accordance with the standard read and write

timing I C, and the maximum speed supported 100Kb / s. Read the temperature and humidity of

example, as shown in Figure 16.

The host sends commands to: START +0 xB8 (SLA) +0 x03 (function code) +0 x00 (starting

address) +0 x04 (register length) + STOP

2

2

2

2

2

2

Aosong Guangzhou Electronics Co., Ltd.

Order Phone: 4006 305378

Enterprise QQ: 4006305378

www.aosong.com