MPXM2102AS datasheet(546/670 Pages) MOTOROLA

546 / 670 page

AN1950

3–400

Motorola Sensor Device Data

www.motorola.com/semiconductors

ALLINIT Function

The ALLINIT function disables the COP for this version of

software, sets the data direction bits, and disables the data to

the LCD and turns off the LCD enable line. It also sets up the

microcontroller’s internal clock to half the speed of the bus

clock. See Section 15, Computer Operating Properly, of the

MC68908QT4 datasheet for information on utilizing the COP

module to help software recover from runaway code.

WARMUP Function

The WARMUP function alternates the blinking of the two

LEDs ten times. This gives the LCD some time to warm up.

Then the function “warmup” calls the LCD initialization

function, “lcdinit”.

bintasc Function

The “binasc” function converts a binary value to its ascii

representation.

A/D Functions

The A/D functions are used to input the amplified voltage

from the pressure sensor from channel 0 of the A/D converter.

The function “adcbyti” will set the A/D control register, wait for

the A/D reading and load the data from the A/D data register

into the accumulator. The function “adcbyta” is used to obtain

an averaged A/D reading by calling “adcbyti” 256 times and

returning the resulting average in the accumulator.

LCD Functions

The LCD hardware is set up for multiplexing 3 pins from the

microcontroller using an 8–bit shift register. Channels 3, 4,

and 5 are used on port A for the LCD enable (E), the LCD reset

(RS), and the shift register clock bit, respectively. The clock

bit is used to manually clock data from channel 4 into the 8–bit

shift register. This is the same line as the LCD RS bit because

the MSB of the data is low for a command and high for data.

The RS bit prepares the LCD for instructions or data with the

same bit convention. When the 8 bits of data are available on

the output pins of the shift register, the LCD enable (E) is

toggled to receive the data.

The LCD functions consist of an initialization function

“lcdinit” which is used once when the system is started and five

output functions. The functions “lcdcmdo” and “lcdchro” both

send a byte of data. The function “shiftA” is called by both

“lcdcmdo” and “lcdchro” to manually shift 8 bits of data into the

shift register.

The function “lcdnibo” converts the data to

binary before displaying. The “lcdbyto” displays a byte of data

by calling “lcdnibo” for each nibble of data. The function

“lcdstro” enables strings to be easily added to the software for

display. The function accepts a comma–delimited string of

data consisting of 1–2 commands for clearing the screen and

positioning the cursor. It then continues to output characters

from the string until the “@” symbol is found, signally the end

of the string.

Conclusion

The water level reference design uses a MPXM2010GS

pressure sensor in the low cost MPAK package, the low cost,

8–pin microcontroller, and a quad op–amp to amplify the

sensor output voltage.

This system uses very few

components, reducing the overall system cost. This allows for

a solution to compete with a mechanical switch for water level

detection but also offer additional applications such as

monitoring water flow for leak detection, and the other

applications for smart washing machines.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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