MPXM2102AS datasheet(369/670 Pages) MOTOROLA

369 / 670 page

AN1305

3–223

Motorola Sensor Device Data

www.motorola.com/semiconductors

Figure 5. DEVB–114 Software Flowchart

YES

START

INITIALIZE DISPLAY I/O PORTS

INITIALIZE TIMER REGISTERS

ALLOW INTERRUPTS

PERFORM AUTO ZERO

TIMER

INTERRUPT

J1 OUT?

ACCUMULATE 100 A/D CONVERSIONS

COMPUTE INPUT PRESSURE

CONVERT TO DECIMAL

PLACE IN RESULT OUTPUT BUFFER

SERVICE TIMER REGISTERS

SETUP COUNTER FOR NEXT INTERRUPT

SERVICE LIQUID CRYSTAL DISPLAY

RETURN FROM INTERRUPT

SLOPE = 64

SLOPE = 63

J2 OUT?

SLOPE = 65

YES

The 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 approximately a 20 ms loop.

read_a2d() Performs one hundred reads on the analog to

digital converter on multiplexer channel 5 and returns the

accumulation.

fixcompare() Services the internal timer for 30 ms timer

compare interrupts.

TIMERCMP() Alternates the data and backplane for the

liquid crystal display.

initio() Sets up the microcomputer’s I/O ports, timer, allows

processor interrupts, and calls adzero().

adzero() This routine is necessary at power–up time

because it delays the power supply and allows the

transducer to 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. It is then output to the display.

display_psi() This routine is called from ‘main()’. The ana-

log to digital converter routine is called, the pressure is

calculated, and the pressure applied to the sensor is dis-

played. The loop then repeats.

main() This is the main routine called from reset. It calls

‘initio()’ to set up 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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