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LDE Series

Digital low differential pressure sensors

www.first-sensor.com

www.sensortechnics.com

Fig. 3: Resistors at both ends of the SPI lines

SPI - SERIAL PERIPHERAL INTERFACE

Introduction

The LDE serial interface is a high-speed synchronous

data input and output communication port. The serial

interface operates using a standard 4-wire SPI bus.

The LDE device runs in SPI mode 0, which requires the

clock line SCLK to idle low (CPOL = 0), and for data to

be sampled on the leading clock edge (CPHA = 0).

Figure 5 illustrates this mode of operation.

Care should be taken to ensure that the sensor is

properly connected to the master microcontroller.

Refer to the manufacturer's datasheet for more

information regarding physical connections.

Application circuit

The use of pull-up resistors is generally unnecessary

for SPI as most master devices are configured for

push-pull mode. If pull-up resistors are required for

use with 3 V LDE devices, however, they should be

greater than 50 k

Ω.

Note: It is important to adhere to the communication protocol in order to avoid damage to the sensor.

There are, however, some cases where it may be

helpful to use 33

Ω series resistors at both ends of the

SPI lines, as shown in Figure 3. Signal quality may be

further improved by the addition of a buffer as shown in

Figure 4. These cases include multiple slave devices

on the same bus segment, using a master device

with limited driving capability and long SPI bus lines.

If these series resistors are used, they must be

physically placed as close as possible to the pins of

the master and slave devices.

Signal control

The serial interface is enabled by asserting /CS low.

The serial input clock, SCLK, is gated internally to

begin accepting the input data at MOSI, or sending

the output data on MISO. When /CS rises, the data

clocked into MOSI is loaded into an internal register.

Fig. 4: Addition of a buffer

SCLK

MOSI

MISO

/CS

SCLK

MOSI

MISO

/CS

Sensor

33

33

33

33

33

33

33

33

SCLK

MOSI

MISO

/CS

SCLK

MOSI

MISO

/CS

Sensor

33

33

33

33

33

33

33

33

33

33

33

33

/OE

/OE

/OE

/OE