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SI7050-A20 Datasheet, PDF (13/26 Pages) Silicon Laboratories – IC TEMPERATURE SENSORS
Si7050/3/4/5-A20
5.1. Issuing a Measurement Command
The measurement command instructs the Si705x to perform a temperature measurement. 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; the chosen
command code determines which mode is used.
Optionally, a checksum byte can be returned from the slave for use in checking for transmission errors. 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.
The checksum byte is optional after initiating a temperature measurement with commands 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.
Table 10. 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 = 0
WRITE
W Write bit = 1
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
Sequencetoperformameasurementandreadbackresult(HoldMasterMode)
S
Slave
Address
W A
Measure
Cmd
A Sr
Slave
Address
R A

Clockstretch
during
measurement
MSByte A LSByte NA P

A Checksum NA P
Rev. 1.0
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