Datasheet SHT20 (Sensirion) - 9

link to page 8 link to page 9 link to page 9 link to page 9 Datasheet SHT20 Resolution RH typ RH max T typ T max Units default and is not recommended for use. Please use Soft 14 bit 66 85 ms Reset instead – it contains OTP Reload. 13 bit 33 43 ms 12 Bit 22 29 17 22 ms Bit # Bits Description / Coding Default 11 bit 12 15 9 11 ms 7, 0 2 Measurement resolution ‘00’ 10 bit 7 9 ms RH T 8 bit 3 4 ms ‘00’ 12 bit 14 bit
Table 7
Measurement times for RH and T measurements at ‘01’ 8 bit 12 bit different resolutions. Typical values are recommended for ‘10’ 10 bit 13 bit calculating energy consumption while maximum values shall be ‘11’ 11 bit 11 bit applied for calculating waiting times in communication. 6 1 Status: End of battery13 ‘0’ Please note: I2C communication allows for repeated Start ‘0’: VDD > 2.25 V conditions (S) without closing prior sequence with Stop ‘1’: VDD < 2.25 V condition (P) – compare Figures 15, 16 and 18. Still, any 3, 4, 5 3 Reserved sequence with adjacent Start condition may alternatively 2 1 Enable on-chip heater ‘0’ be closed with a Stop condition. 1 1 Disable OTP Reload ‘1’
5.5 Soft Reset Table 8
User Register. Cut-off value for End of Battery signal may vary by ±0.1 V. Reserved bits must not be changed. “OTP This command (see Table 6) is used for rebooting the reload” = ‘0’ loads default settings after each time a sensor system without switching the power off and on measurement command is issued. again. Upon reception of this command, the sensor system reinitializes and starts operation according to the An example for I2C communication reading and writing the default settings – apart from the heater bit in the user User Register is given in Figure 18. 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 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 CK 1 1 1 0 0 1 1 1 CK A A S 1 0 0 0 0 0 0 0 CKA 1 1 1 1 1 1 1 0 CKA P I2C address + write Read Register I2C address + write Soft Reset 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K
Figure 17
Soft Reset – grey blocks are controlled by SHT2x. S 1 0 0 0 0 0 0 1 CKA 0 0 0 0 0 0 1 0 ACN I2C address + read Register content
5.6 User Register
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 The content of User Register is described in Table 8. S 1 0 0 0 0 0 0 0 CK 1 1 1 0 0 1 1 0 CK Please note that reserved bits must not be changed and A A default values of respective reserved bits may change I2C address + write Write Register over time without prior notice. Therefore, for any writing to 55 56 57 58 59 60 61 62 63 the User Register, default values of reserved bits must be read first. Thereafter, the full User Register string is 0 0 0 0 0 0 1 1 CKA P composed of respective default values of reserved bits Register content to be writ en and the remainder of accessible bits optionally with default
Figure 18
Read and write register sequence – grey blocks are or non-default values. controlled by SHT2x. In this example, the resolution is set to 8bit The end of battery alert is activated when the battery / 12bit. power falls below 2.25 V.
5.7 CRC Checksum
The heater is intended to be used for functionality SHT2x provides a CRC-8 checksum for error detection. diagnosis – relative humidity drops upon rising The polynomial used is x8 + x5 + x4 +1. For more details temperature. The heater consumes about 5.5mW and and implementation please refer to the application note provides a temperature increase of about 0.5 – 1.5°C. “CRC Checksum Calculation for SHT2x”. OTP Reload is a safety feature and loads the entire OTP settings to the register, with the exception of the heater bit, before every measurement. This feature is disabled per 13 This status bit is updated after each measurement www.sensirion.com Version 5 – October 2022 9/14