ND Series

Industrial Middle Pressure Sensors

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9

The requirement to send the Mode and Rate bytes on each data read cycle is intentional. The purpose is to force the master to send

specific data for each communication and prevent inadvertent data from being sent to the sensor. Since a SPI interface will generally

re-circulate data through its shift register, the intention is to prevent the pressure output from the sensor from being re-circulated

back to the sensor and potentially causing unintended corruption of the intended mode register.

10.4 I2C Interface

The ND Series is compatible with the I2C protocol. For detailed information regarding the I2C protocol, please refer to the Philips I2C

Bus Specification, Version 2.

10.4.1 I2C Address

The I2C address is set to 0x28 by grounding the SCK line. Other I2C addresses can be established

by applying a voltage to the SCK line by use of a resistor divider across the sensor supply

voltage. The suggested resistor values and the respective I2C address are shown in the table to

the left.

Note: R1 is the lower resister of the divider where R2 is the upper resistor of the divider.

10.4.2 I2C Communications Model

The sensor is configured as a slave device and as such,

the communicating host must be configured as a master.

There are two types of possible data transfers, data

transfers from the master transmitter to an addressed

sensor (WRITE), and data transfers from an addressed

sensor to a master receiver (READ). The master device

initiates both types of data transfers and provides the

serial clock pulses on SCL.

The communications model for I2C is similar to that of SPI

however, since I2C is a half-duplex protocol, the transfer

of information to and from the sensor is separated into

two separate communications. This is in contrast to the

SPI interface where the transmitted and received data

occurs simultaneously to and from the host. Refer to the

figure to the right for the data communication model for

the ND Series sensors.

User Mode Byte

SCK

MOSI

MISO

nSS

Pressure Output High Byte

User Rate Byte

Pressure Output Low Byte

SPI Data Diagram

R1 (kΩ) R2 (kΩ) Address

(decimal)

Address

(hex)

120

5.6

49

0x31

120

12

48

0x30

120

27

47

0x2F

120

51

46

0x2E

120

100

45

0x2D

56

100

44

0x2C

30

100

43

0x2B

15

100

42

0x2A

5.6

100

41

0x29

0

NoPop

40

0x28

I2C Address Selection Table