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参数资料
| 型号： | 1-100645-01 |
| 厂商： | SENSITRON SEMICONDUCTOR |
| 元件分类： | 温度/湿度传感器 |
| 英文描述： | DIGITAL TEMP SENSOR-SERIAL, 14BIT(s), SQUARE, SURFACE MOUNT |
| 封装： | ROHS COMPLIANT PACKAGE, 6 PIN |
| 文件页数： | 12/12页 |
| 文件大小： | 332K |
| 代理商： | 1-100645-01 |
Datasheet SHT21
www.sensirion.com
Version 1.1 – May 2010
9/12
5.5
Soft Reset
This command (see Table 6) is used for rebooting the
sensor system without switching the power off and on
again. Upon reception of this command, the sensor
system reinitializes and starts operation according to the
default settings – with the exception of the heater bit in the
user register (see Sect. 5.6). The soft reset takes less than
15ms.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
S 1 0 0 0 0 0 0 0
AC
K
1 1 1 1 1 1 1 0
AC
K
P
I2C address + write
Soft Reset
Figure 17 Soft Reset – grey blocks are controlled by SHT2x.
5.6
User Register
The content of User Register is described in Table 8.
Please note that reserved bits must not be changed and
default values of respective reserved bits may change
over time without prior notice. Therefore, for any writing to
the User Register, default values of reserved bits must be
read first. Thereafter, the full User Register string is
composed of respective default values of reserved bits
and the remainder of accessible bits optionally with default
or non-default values.
Bit
# Bits
Description / Coding
Default
7, 0
2
Measurement resolution
RH
T
‘00’
12 bit
14 bit
‘01’
8 bit
12 bit
‘10’
10 bit
13 bit
‘11’
11 bit
‘00’
6
1
Status: End of battery15
‘0’: VDD > 2.25V
‘1’: VDD < 2.25V
‘0’
3, 4, 5
3
Reserved
2
1
Enable on-chip heater
‘0’
1
Disable OTP Reload
‘1’
Table 8 User Register. Cut-off value for End of Battery signal
may vary by ±0.05V. Reserved bits must not be changed. “OTP
reload” = ‘0’ loads default settings after each time a
measurement command is issued.
The end of battery alert is activated when the battery
power falls below 2.25V.
The heater is intended to be used for functionality
diagnosis
–
relative
humidity
drops
upon
rising
temperature. The heater consumes about 5.5mW and
provides a temperature increase of about 0.5 – 1.5°C.
OTP Reload is a safety feature and loads the entire OTP
settings to the register, with the exception of the heater bit,
15 This status bit is updated after each measurement
before every measurement. This feature is disabled per
default and is not recommended for use. Please use Soft
Reset instead – it contains OTP Reload.
An example for I2C communication reading and writing the
User Register is given in Figure 18.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
S 1 0 0 0 0 0 0 0
AC
K
1 1 1 0 0 1 1 1
AC
K
I2C address + write
Read Register
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
S 1 0 0 0 0 0 0 1
AC
K
0 0 0 0 0 0 1 0
N
A
C
K
I2C address + read
Register content
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53 54
S 1 0 0 0 0 0 0 0
AC
K
1 1 1 0 0 1 1 0
AC
K
I2C address + write
Write Register
55
56
57
58
59
60
61
62
63
0 0 0 0 0 0 1 1
AC
K
P
Register content to be written
Figure 18 Read and write register sequence – grey blocks are
controlled by SHT2x. In this example, the resolution is set to 8bit
/ 12bit.
5.7
CRC Checksum
CRC8 is a well known standard checksum concept. For
implementation please refer to public sources such as
Wikipedia.
5.8
Serial Number
SHT21 provides an electronic identification code. For
instructions on how to read the identification code please
refer to the Application Note “Electronic Identification
Code” – to be downloaded from the web page
www.sensirion.com/SHT21.
6 Conversion of Signal Output
Default resolution is set to 12 bit relative humidity and 14
bit temperature reading. Measured data are transferred in
two byte packages, i.e. in frames of 8 bit length where the
most significant bit (MSB) is transferred first (left aligned).
Each byte is followed by an acknowledge bit. The two
status bits, the last bits of LSB, must be set to ‘0’ before
calculating physical values. In the example of Figure 15
and Figure 16, the transferred 16 bit relative humidity data
is ‘0110’0011’0101’0000’ = 25424.
6.1
Relative Humidity Conversion
With the relative humidity signal output SRH the relative
humidity RH is obtained by the following formula (result in
%RH), no matter which resolution is chosen:
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