Cirrus-logic AN131 Manual do Utilizador descarregar pdf (Página 11)

AN131

AN131REV2 11

JSR send_spi ;Transfer low byte

RTS ;Return

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

;* Routine - read_register

;* Input - COMMAND

;* Output - HIGHBYTE, MIDBYTE, LOWBYTE

;* This subroutine is used to read from the internal registers of the

;* CS5521/22/23/24/28

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

read_register LDA COMMAND ;Load ACCA with COMMAND

JSR send_spi ;Send command byte

JSR receive_spi ;Receive a byte

STA HIGHBYTE ;Store value in HIGHBYTE

JSR receive_spi ;Receive a byte

STA MIDBYTE ;Store value in MIDBYTE

JSR receive_spi ;Receive a byte

STA LOWBYTE ;Store value in LOWBYTE

RTS ;Return

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

;* Routine - send_spi

;* Input - Byte to be send is placed in ACCA

;* Output - none

;* This subroutine sends a byte to the ADC using the SPI port.

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

send_spi STA SPDR ;Move ACCA to the SPI Data Register

wait0: BRCLR SPIF,SPSR,wait0 ;Loop until byte has been transmitted

RTS ;Return

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

;* Routine - receive_spi

;* Input - none

;* Output - Received byte is placed in ACCA

;* This subroutine receives a byte from the ADC using the SPI port

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

receive_spi CLRA ;Load ACCA Register with all Zeros

STA SPDR ;Transfer 8 0’s to clock next byte

wait1: BRCLR SPIF,SPSR,wait1 ;Reset SPIF bit

LDA SPDR ;Get received information

RTS ;Return

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

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Cirrus-logic AN131 Manual do Utilizador Página 11