MPXM2102AS datasheet(489/670 Pages) MOTOROLA

489 / 670 page

AN1551

3–343

Motorola Sensor Device Data

www.motorola.com/semiconductors

SOFTWARE EXAMPLES

The following example listings show how a user may

communicate with the smart sensor via a master MCU. The

software example shown assumes that the master MCU is an

MC68HC11. Any MCU with the proper I/O functionality will

operate similarly with the smart sensor system.

When using parallel I/O instead of an SPI port to interface

the smart sensor, the user must “bit bang” the clock and data

out of the parallel I/O, so as to simulate the SPI port. As long

as the timing relationships of data and clock follow those of

Figure 3 (see also Table 3), the smart sensor will function

properly when interfaced to a processor with a parallel type

interface. In the following two code examples, the sensor unit

is interfaced to the master MCU via the SPI port, and the

sensor’s CS input is connected to the HC11’s Port D pin 5.

This example is coded in ‘C’ for the MC68HC11:

/* FIRST INITIALIZE THE I/O (INCLUDE A HEADER FILE TO INCLUDE I/O DEFINITIONS) */

void init_io(void)

{

PORTD = 0X29; /* SS* PD5 = 1, PD3 = 1, PD0 = 1 */

DDRD = 0X3B; /* SS* PD5 = 1, PD3 = 1, PD1 = 1, PD0 = 1 */

SPCR = 0X5E; /* ENABLE THE SPI, MAKE MCU THE MASTR, SCK = E CLK /4 */

/* I/O INITIALIZATION IS COMPLETE */

}

/* WE NEED A FUNCTION TO WRITE TO AND READ FROM THE SPI */

write_spi(char data)

{

SPDR = data; /* WRITE THE DATA TO THE SPI DATA PORT */

while( ! (SPSR & 0x80 )); /* WAIT UNTIL DATA HAS SHIFTED OUT OF AND

BACK INTO THE SPI */

return(SPDR): /* RETRIEVE THE RESULTS OF THE LAST COMMAND TO

THE SENSOR AND RETURN */

}

/* NOW WE NEED TO CALL THE ABOVE */

void main(void)

{

char rtn_data; /* rtn_data IS THE RETURNED DATA FROM THE SENSOR */

init_io();

while(1) /* JUST LOOP FOREVER */

rtn_data = write_spi(0x01); /* 0x01 IS THE COMMAND TO THE SENSOR

THAT REQUESTS PRESSURE. THE VALUE IN

rtn_data WILL BE IN THE RANGE OF

0..0XFF = 0..100% FULL SCALE PRESSURE THE

SECOND TIME THROUGH THE LOOP. THE INITIAL

TIME THROUGH THE LOOP, THE DATA

RETURNED IS INDETERMINATE */

}

The next example is coded in assembly for the MC68HC11:

* PORT OFFSETS INTO THE I/O MAP

PORTS

EQU

$1000

ASSUME THE I/O STARTS AT $1000

PORTD

EQU

DDRD

EQU

SPCR

EQU

SPSR

EQU

$29

SPDR

EQU

$2A

ORG

$E000

* FIRST INITIALIZE THE I/O

INITIO

LDX

#PORTS

BASE ADDRESS OF THE I/O

LDAA

#$29

STAA

PORTD,X

SS* PD5 = 1, PD3 = 1, PD0 = 1

LDAA

#$3B

STAA

DDRD,X

SS* PD5 = 1, PD3 = 1, PD1 = 1, PD0 = 1

LDAA

#$5E

STAA

SPCR,X

ENABLE THE SPI, MAKE MCU THE MASTR,

SCK = E CLK /4

RTS

I/O INITIALIZATION IS COMPLETE

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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