STSC1 datasheet(6/13 Pages) ETC2

6 / 13 page

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Version 1 – May 2014

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6.1 Power-Up and Communication Start

Upon VDD reaching the power-up voltage level VPOR, the

STSC1 enters idle state after a duration of tPU. In idle

state, the STSC1 is ready to receive commands from the

master (microcontroller).

Each transmission sequence begins with START condition

(S) and ends with an (optional) STOP condition (P) as

described in the I2C-bus specification. Whenever the

sensor is powered up, but not performing a measurement

or communicating, it automatically enters idle state for

energy saving.

Please note that in case VDD is set to 0 V (GND), e.g. in

case of a power off of the STSC1, the SCL and SDA pads

are also pulled to GND. Consequently, the I2C bus is

blocked while VDD of the STSC1 is set to 0 V.

6.2 Measurement Commands

The STSC1 provides the possibility to define the sensor

behavior during measurement (see Table 8).

Clock Stretching

Enabled

Clock Stretching

Disabled

0x7CA2

0x7866

Table 8 Measurement commands.

6.3 Starting a Measurement

A measurement communication sequence consists of a

START condition followed by the I2C header with the 7-bit

I2C device address and a write bit (write W: ‘0’). The

sensor indicates the proper reception of a byte by pulling

the SDA pin low (ACK bit) after the falling edge of the 8th

SCL clock. Then the sensor is ready to receive a 16-bit

measurement command. Again, the STSC1 acknowledges

the proper reception of each byte with ACK condition. A

complete measurement cycle is presented in Figure 5.

With the acknowledgement of the measurement

command, the STSC1 starts measuring temperature.

6.4 Sensor Behavior during Measurement and

Clock Stretching

In general, the sensor does not respond to any I2C activity

during measurement, i.e. I2C read and write headers are

not acknowledged (NACK). However, when clock

stretching has been enabled by using a corresponding

measurement command, the sensor responds to a read

header with an ACK and subsequently pulls down the SCL

line until the measurement is complete. As soon as the

measurement is complete, the sensor starts sending the

measurement results.

During measurement, the sensor has a current

consumption according to Table 2.

For

best

possible

repeatability

temperature

measurements, it is recommended to avoid any

communication on the I2C bus while the STSC1 is

measuring. For more information, see application note

“SHTC1 Optimization of Repeatibility”.

6.5 Readout of Measurement Results

After a measurement command has been issued and the

sensor has completed the measurement, the master can

read the measurement results by sending a START

condition followed by an I2C read header. The sensor will

acknowledge the reception of the read header and send

two bytes of temperature data followed by one byte CRC

checksum. Each byte must be acknowledged by the

microcontroller with an ACK condition for the sensor to

continue sending data. If the STSC1 does not receive an

ACK from the master after any byte of data, it will not

continue sending data.

The I2C master can abort the read transfer with a NACK

condition after any data byte if it is not interested in

subsequent data, e.g. the CRC byte, in order to save time.

6.6 Soft Reset

The STSC1 provides a soft reset mechanism that forces

the system into a well-defined state without removing the

power supply. If the system is in idle state (i.e. if no

measurement is in progress) the soft reset command can

be sent to STSC1 according to Figure 6. This triggers the

sensor to reset all internal state machines and reload

calibration data from the memory.

Command

Hex. Code

Bin. Code

Software reset

0x805D

1000’0000’0101’1101

Table 9 Soft reset command.

6.7 Read-out of ID Register

The STSC1 has an ID register which contains an STSC1-

specific product code. The read-out of the ID register can

be used to verify the presence of the sensor and proper

communication. The command to read the ID register is

shown in Table 10.

Command

Hex. Code

Bin. Code

Read ID register

0xEFC8

1110’1111’1100’1000

Table 10 Read-out command of ID register.

It needs to be sent to the STSC1 after an I2C write header.

After the STSC1 has acknowledged the proper reception

of the command, the master can send an I2C read header

and the STSC1 will submit the 16-bit ID followed by 8 bits

of CRC. The structure of the ID is described in Table 11.

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