MPX2202DP datasheet(395/670 Pages) MOTOROLA

395 / 670 page

AN1315

3–249

Motorola Sensor Device Data

www.motorola.com/semiconductors

Figure 5. DEVB–158 Software Flowchart

TIMER

INTERRUPT

SERVICE TIMER REGISTERS

SETUP COUNTER FOR NEXT INTERRUPT

SERVICE LIQUID CRYSTAL DISPLAY

RETURN

ACCUMULATE 100 A/D CONVERSIONS

COMPUTE INPUT PRESSURE

CONVERT TO DECIMAL/SEGMENT DATA

PLACE IN RESULT OUTPUT BUFFER

COMPUTE SLOPE CONSTANT

INITIALIZE DISPLAY I/O PORTS

INITIALIZE TIMER REGISTERS

DETERMINE SENSOR TYPE

ENABLE INTERRUPTS

START

The “C” compiler used in this project was provided by BYTE

CRAFT LTD. (519) 888–6911. A compiler listing of the

program is included at the end of this document. The following

is a brief explanation of the routines:

delay()

Used to provide a software loop delay.

read_a2d()

Performs 100 reads on the A/D converter on

multiplexer channel 0 and returns the accumulation.

fixcompare()

Services the internal timer for 15 ms. timer

compare interrupts.

TIMERCMP()

Alternates the data and backplane inputs to

the liquid crystal display.

initio()

Sets up the microprocessor’s I/O ports, timer and

enables processor interrupts.

adzero()

This routine is called at powerup time. It delays

to let the power supply and the transducer stabilize. It then

calls “read_atod()” and saves the returned value as the

sensors output voltage with zero pressure applied.

cvt_bin_dec(unsigned long arg)

This routine converts

the unsigned binary argument passed in “arg” to a five

digit decimal number in an array called “digit.” It then uses

the decimal results for each digit as an index into a table

that converts the decimal number into a segment pattern

for the display. This is then output to the display.

display_psi()

This routine is called from “main()” never to

return. The A/D converter routine is called, the pressure

is calculated based on the type sensor detected and the

pressure applied to the sensor is displayed. The loop

then repeats.

sensor_type()

This routine determines the type of sensor

from reading J1 to J3, setting the full scale pressure for

that particular sensor in a variable for use by display_psi().

sensor_slope()

This routine determines the slope

constant to be used by display_psi() for engineering units

output.

main()

This is the main routine called from reset. It calls

“initio()” to setup the system’s I/O. “display_psi()” is called

to compute and display the pressure applied to the

sensor.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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