MPXM2102AS datasheet(442/670 Pages) MOTOROLA

442 / 670 page

AN1326

3–296

Motorola Sensor Device Data

www.motorola.com/semiconductors

Purpose is to implement a Look–Up conversion

The BCD is used to index off of TABLE

where the appropriate hex code to display

that decimal digit is contained.

DIGIT4,3,2 are converted only.

LOOKUP

LDX

#DIGIT1+4

* Counter starts at 5

TABLOOP

DEX

* Start with Digit4

LDY

#TABLE

* Loads table base into Y–pointer

LDAB

0,X

* Loads current digit into B

ABY

* Adds to base to index off TABLE

LDAA

0,Y

* Stores HEX segment result in A

STAA

0,X

CPX

#DIGIT2

* Loop condition complete, DIGIT2 Converted

BNE

TABLOOP

RTS

Subroutine SPI2LCD

Purpose is to output digits to LCD via SPI

The format for this is to send a start byte,

four digits, and a stop byte. This system

will have 3 significant digits: blank digit

and three decimal digits.

Sending LCD Start Byte

SPI2LCD

LDX

#REGBASE

LDAA

SPSR,X

* Reads to clear SPIF flag

LDAA

#$02

* Byte, no colon, start bit

BSR

TRANSFER

* Transmit byte

Initializing decimal point & blank digit

LDAA

DIGIT3

* Sets MSB for decimal pt.

ORA

#$80

* after digit 3

STAA

DIGIT3

LDAA

#$00

* Set 1st digit as blank

STAA

DIGIT1

Sending four decimal digits

LDY

#DIGIT1

* Pointer set to send 4 bytes

DLOOP

LDAA

0,Y

* Loads digit to be x–mitted

BSR

TRANSFER

* Transmit byte

INY

* Branch until both bytes sent

CPY

#DIGIT4+1

BNE

DLOOP

Sending LCD Stop Byte

LDAA

#$00

* end byte requires all 0’s

BSR

TRANSFER

* Transmit byte

RTS

Subroutine TRANSFER

Purpose is to send data bits to SPI

and wait for conversion complete flag bit to be set.

TRANSFER LDX

#REGBASE

BCLR

PORTD,X #$20

* Assert SS Line to start X–misssion

STAA

SPDR,X

* Load Data into Data Reg.,X–mit

XMIT

BRCLR

SPSR,X

#$80 XMIT * Wait for flag

BSET

PORTD,X #$20

* DISASSERT SS Line

LDAB

SPSR,X

* Read to Clear SPI Flag

RTS

Location for FCB memory for look–up table

There are 11 possible digits: blank, 0–9

TABLE

FCB

$7E,$30,$6D,$79,$33,$5B,$5F,$70,$7F,$73,$00

END

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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