Datasheet SHT1x
Communication terminates after the acknowledge bit of
the CRC data. If CRC-8 checksum is not used the
controller may terminate the communication after the
measurement data LSB by keeping ACK high. The device
automatically returns to Sleep Mode after measurement
and communication are completed.
3.6 Status Register
Some of the advanced functions of the SHT1x such as
selecting measurement resolution, end-of-battery notice,
use of OTP reload or using the heater may be activated by
sending a command to the status register. The following
section gives a brief overview of these features.
Important: To keep self heating below 0.1°C, SHT1x
should not be active for more than 10% of the time – e.g.
maximum one measurement per second at 12bit accuracy
shall be made.
After the command Status Register Read or Status
Register Write – see Table 4 – the content of 8 bits of the
status register may be read out or written. For the
communication compare Figure 14 and Figure 15 – the
assignation of the bits is displayed in Table 5.
3.4 Connection reset sequence
If communication with the device is lost the following signal
sequence will reset the serial interface: While leaving
DATA high, toggle SCK nine or more times – see Figure
13. This must be followed by a Transmission Start
sequence preceding the next command. This sequence
resets the interface only. The status register preserves its
content.
0 0 0 0 0 1 1 0
Status Register
Figure 14: Status Register Write
0 0 0 0 0 1 1 1
Status Register
Checksum
Figure 15: Status Register Read
80%
3
9
1
2
4 - 8
SCK
Examples of full communication cycle are displayed in
Figure 16 and Figure 17.
20%
Transmission Start
80%
20%
Wait for
DATA ready
DATA
0 0 0 Command
0 0
MSB
Figure 13: Connection Reset Sequence
LSB
Checksum
3.5 CRC Checksum calculation
The whole digital transmission is secured by an 8bit
checksum. It ensures that any wrong data can be detected
and eliminated. As described above this is an additional
feature of which may be used or abandoned. Please
consult Application Note “CRC Checksum” for information
on how to calculate the CRC.
Figure 16: Overview of Measurement Sequence. TS = Trans-
mission Start, MSB = Most Significant Byte, LSB = Last
Significant Byte, LSb = Last Significant Bit.
Transmission Start
Address = ‘000’
Command = ‘00101’
Measurement
(80ms for 12bit)
A2
A1 A0
C4 C3
C2 C1
C0 ACK
SCK
Sensor pulls DATA line low after
completion of measurement
ACK
A2
A1
A0 C4
C3
C2 C1 C0
DATA
Skip ACK to end transmission
(if no CRC is used)
12bit Humidity Data
ACK
Idle Bits
15 14 13
MSb
11
LSb
0
12
10
9
8
7
6
5
4
3
2
1
ACK
SCK
ACK
ACK
15
14
13
12
10
9
8
7
6
5
4
3
2
1
0
11
DATA
Sleep (wait for next
measurement)
Transmission Start
CRC-8 Checksum
LSb
0
MSb
7
6
5
4
3
2
1
ACK
SCK
7
6
5
4
3
2
1
0
ACK
DATA
Figure 17: Example RH measurement sequence for value “0000’0100“0011’0001” = 1073 = 35.50%RH (without temperature
compensation). DATA valid times are given and referenced in boxes on DATA line. Bold DATA lines are controlled by sensor while plain
lines are controlled by the micro-controller.
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