Motorola MCU 68HC912 Manual do Utilizador descarregar pdf (Página 11)

SLAA108A

SPI-Based Data Acquisition/Monitor Using the TLC2551 Serial ADC 11

BSR INIT ; Subroutine to initialize SPI registers

BSR SAMPLE ; Subroutine to start transmission

;* ----------------------------------------------------------------------

;* Initialization Subroutine

;* ----------------------------------------------------------------------

INIT:

BSET DDRS, #%11101100 ; Configure PORT S input/ouput:

; SS/CS, SCK, MOSI, MISO, PS3, PS2, TXD, RXD

BSET SP0BR, #%00000000 ; Set Baud Rate

BSET SP0CR1, #%01010100 ; Configure SPI(SP0CR1):

; SPIE, SPE, SWOM, MSTR, CPOL, CPHA, SSOE, LSBF

BSET SP0CR2, #%00000000 ; Configure SPI(SP0CR2):

; -,-,-,-,-,-,SSWAI, SPCO

MOVB #$00, UPPER_BYTE

MOVB #$00, LOWER_BYTE

RTS

;* -------------------------------------------

;* Sample / Convert

;* -------------------------------------------

SAMPLE:

MOVB #$00, PORTS ; Sets ADC CS Lo

MOVB #$00, SP0DR ; Write zero value to data register

; to generate SCLK for ADC

BSR FLAG ; Clear SPIF

LDAA SP0DR ; Load first ADC Sample

MOVB #$00, SP0DR ; Write zero value to data register

; to generate SCLK for ADC

BSR FLAG ; Clear SPIF

LDAB SP0DR ; Load second ADC Sample

STD DATA ; Store ACCA and ACCB in Data

;* ----------------------------------------------------------------------

;* Data Shifting Subroutine

;* ----------------------------------------------------------------------

LDX #$0004 ; Shift data four bits to

; bypass DAC config registers

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Motorola MCU 68HC912 Manual do Utilizador Página 11