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Figure 3 Timing diagram for digital input/output pads. SDA directions are seen from the sensor. Bold SDA lines are controlled by the

sensor, plain SDA lines are controlled by the micro-controller. Note that SDA valid read time is triggered by falling edge of preceding toggle.

5 Interface Specifications

from 0 to 400 kHz) with clock stretching. For detailed

specification and user manual UM10204, Rev. 4,

February 13, 2012:

http://ics.nxp.com/support/documents/interface/pdf/I2C.bu

s.specification.pdf

The STSC1 comes in a 4-pin package – see Table 6.

Pin Name

Comments

1

VDD Supply voltage

2

SCL Serial clock, bidirectional

3

SDA Serial data, bidirectional

4

VSS Ground

Table 6 STSC1 pin assignment (top view). The center pad is

internally connected to VSS.

Power-supply pins supply voltage (VDD) and ground

(VSS) must be decoupled with a 100 nF capacitor that

shall be placed as close to the sensor as possible – see

Figure 4.

SCL is used to synchronize the communication between

microcontroller and the sensor. The master must keep the

clock frequency within 0 to 400 kHz as specified in Table

5. The STSC1 may pull down the SCL line when clock

stretching is enabled.

The SDA pin is used to transfer data in and out of the

sensor. For safe communication, the timing specifications

To avoid signal contention, the microcontroller must only

drive SDA and SCL low. External pull-up resistors (e.g.

dimensioning resistor sizes please take bus capacity

requirements into account. It should be noted that pull-up

resistors may be included in I/O circuits of

microcontrollers.

Figure 4 Typical application circuit, including pull-up resistors

For good performance of the STSC1 in the application, it is

important to know that the center pad of the STSC1 offers

the best thermal contact to the temperature sensor. For

more information on design-in, please refer to the

document “SHTxx Design Guide”.

For mechanical reasons the center pad should be

soldered. Electrically, the center pad is internally

connected to GND and may be connected to the GND net

on the PCB or left floating.

6 Operation and Communication

All commands and memory locations of the STSC1 are

mapped to a 16-bit address space which can be accessed

STSC1

Bin.

Dec.

Hex.

100’1010

74

0x4A

Table 7 STSC1

SCL

70%

30%

SDA

70%

30%

DATA IN

SDA

70%

30%

DATA OUT

2

1

3

4

STSC1

AXY89

SDA

SCL

GND

VDD

MCU (master)

R

P

R

P

SCL OUT

SDA OUT

SDA IN

SCL IN

STSC1

(slave)