SI7013-A20 Datasheet, PDF (22/45 Pages) Silicon Laboratories – IC HUMIDITY AND TWO-ZONE TEMPERATURE SENSOR

Si7013-A20
5.1. Issuing a Measurement Command
The measurement commands instruct the Si7013 to perform one of four possible measurements; Relative
Humidity, Temperature, Auxiliary Temperature, or Analog Voltage. While the measurement is in progress, the
option of either clock stretching (Hold Master Mode) or Not Acknowledging read requests (No Hold Master Mode)
is available to indicate to the master that the measurement is in progress. For Humidity and Temperature
measurements, the chosen command code determines which mode is used. For Auxiliary Temperature and
Analog Voltage measurements, No Hold Master mode can be enabled by writing a "1" to bit D6 in register 2. Note
that internal Humidity and Temperature measurements should not be made with this bit set.
Optionally, a checksum byte can be returned from the slave for use in checking for transmission errors for Relative
Humidity and Temperature measurements. The checksum byte is optional after initiating an RH or temperature
measurement with commands 0xE5, 0xF5, 0xE3 and 0xF3. The checksum byte is required for reading the
electronic ID with commands 0xFA 0x0F and 0xFC 0xC9. For all other commands, the checksum byte is not
supported. The checksum byte will follow the least significant measurement byte if it is acknowledged by the
master. The checksum byte is not returned if the master “not acknowledges” the least significant measurement
byte. The checksum byte is calculated using a CRC generator polynomial of x⁸ + x⁵ + x⁴ + 1 with an initialization of
0x00.
Table 15. I²C Bit Descriptions
Name
Symbol
Description
START
S SDA goes low while SCL high.
STOP
P SDA goes high while SCL high.
Repeated START
READ
Sr SDA goes low while SCL high. It is allowable to generate a STOP before the
repeated start. SDA can transition to high before or after SCL goes high in
preparation for generating the START.
R Read bit = 1
WRITE
W Write bit = 0
All other bits
— SDA value must remain high or low during the entire time SCL is high (this is
the set up and hold time in Figure 1).
In the I²C sequence diagrams in the following sections, bits produced by the master and slave are color coded as
shown:
Master
Slave
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Rev. 1.1