Cirrus-logic AN88 Instrukcja Użytkownika Pobierz pdf (Strona 11)

AN88

AN88Rev2 11

;*************************************************************************************

;* Routine - send_spi

;* Input - Byte to be transmitted is placed in W

;* Output - None

;* This subroutine sends a byte to the ADC.

;*************************************************************************************

send_spi: MOVWF SPDR ; Move W to SPDR

MOVLW 0x08 ; Set COUNT to count to 8

MOVWF COUNT ; to transmit byte out SPI

BCF PORTA,SCLK ; Clear SCLK

wait0 ; Send Bit

RLF SPDR,1 ; Rotate SPDR, send MSB 1st

BTFSC STATUS,CARRY_BIT ; If bit low skip next instruct.

BSF PORTA,SDI ; Set SDI

BTFSS STATUS,CARRY_BIT ; If bit high, skip next instruct.

BCF PORTA,SDI ; Clear SDI

BSF PORTA,SCLK ; Toggle Clock

BCF PORTA,SCLK

DECFSZ COUNT,1 ; Loop until byte is transmitted

goto wait0

BCF PORTA,SDI ; Return Pin low

RETURN ; Exit Subroutine

;*************************************************************************************

;* Routine - receive_spi

;* Input - none

;* Output - Byte received is placed in W

;* This subroutine receives a byte from the ADC.

;*************************************************************************************

receive_spi: MOVLW 0x08 ; Set COUNT to count to 8

MOVWF COUNT ; to transmit byte out SPI

BCF PORTA,SCLK ; Clear SCLK

wait1: ; Receive bit

BTFSC PORTA,SDO ; If bit low skip next instruct.

BSF STATUS,CARRY_BIT ; Set SDI

BTFSS PORTA,SDO ; If bit high, skip next instruct.

BCF STATUS,CARRY_BIT ; Clear SDI

RLF SPDR,1 ; Rotate SPDR, Receive MSB 1st

BSF PORTA,SCLK ; Toggle Clock

BCF PORTA,SCLK

DECFSZ COUNT,1 ; Loop until byte is transmitted

goto wait1

MOVF SPDR,0 ; Put byte attained in W

RETURN ; Exit Subroutine

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Cirrus-logic AN88 Instrukcja Użytkownika Strona 11

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