HCE Series

Miniature amplified pressure sensors

5/11

E / 11652 / F

www.first-sensor.com

www.sensortechnics.com

Fig. 2:

3 byte data stream between HCE sensor and master containing the pressure value as a 15 bit information

SPI - SERIAL PERIPHERAL INTERFACE

Fig. 1:

Example of a standard 1 byte SPI data transfer for CPHA=0 and CPOL=0

For further information please refer to

First Sensor's SPI bus application note

Introduction

The HCE is capable to generate a digital output signal.

The device runs a cyclic program, which will store a corrected

sensor value with 14 bit resolution about every 500 µs within

the output registers of the internal ASIC. This cyclic program

runs independent from the bus communication. In order to

use the pressure sensor for digital signal readout, it should

be connected to a SPI Master device.

SPI specifies four signals: The clock (CLK) is generated by

the master and input to all slaves. MOSI carries data from

master to slave. MISO carries data from slave back to

master. A slave select line (SS) allows individual selection

of a slave device.

SPI Modes

A pair of parameters called clock polarity (CPOL) and clock

phase (CPHA) determine the edges of the clock signal on

which the data are driven and sampled. Each of the two

parameters has two possible states, which allows for four

possible combinations, all of which are incompatible with

one another.

In general the HCE series supports all combinations of

clock phase (CPHA) and polarity (CPOL). By default it is

programmed to CPHA = 0 and CPOL = 0, which means

that data transmission starts with the rising first clock edge

(see Fig 1).

Slave select

The falling edge of the SS line indicates the beginning of

the transfer. Additionally the SS line must not be negated

and reasserted between the three bytes to be transmitted.

Data operation

The MOSI line should always be set to high level. So there

is no data transmission from master to slave. Because of

internal configuration the slave will answer the first byte

with an FFxh. The second and third byte contain the 15 bit

pressure information (see Fig. 2).

Relevant data

Data Byte 2

Data Byte 3

X P14 P13 P12 P11 P10 P9 P8 P7 P6 P5 P4 P3 P2 P1 P0

X

X

X

X

X

X

X

X

Data Byte 1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

MOSI

MISO

SCK cycle

1

2

3

4

5

6

7

8

SCK

(CPOL=0)

MOSI

MISO

SS

MSB

LSB

LSB

MSB

Sampling