Cirrus Logic AN131 - Manual (Page 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
;*****************************************************************************