Cirrus Logic AN89 - Manual (Page 7)

AN89
AN89Rev2 7
**************************************************************************************
* Subroutines
**************************************************************************************
**************************************************************************************
* Routine - initialize
* Input
- none
* Output - none
* This subroutine initializes port D for interfacing to the CS5525/6/9 ADC.
* It provides a time delay for oscillator start-up/wake-up period.
* A typical start-up time for a 32768 Hz crystal, due to high Q, is 500 ms.
* Also 1003 XIN clock cycles are allotted for the ADC’s power on reset.
**************************************************************************************
initialize
LDA #%01010000 ; Load ACCA with for SPSC
STA SPCR ; Setup SPI
LDA #40 ; Load ACCA with delay count
JSR delay ; Delay, Power on Reset 1003 XIN
LDA #220 ; Load ACCA with delay count
JSR delay ; Delay, Oscillator start-up 170 mS
JSR delay ; Delay, Oscillator start-up 170 mS
JSR delay ; Delay, Oscillator start-up 170 mS
LDX #$0F ; Reset Serial Port on ADC
LDA #$FF ; Load ACCA with $FF
loop JSR send_spi ; Move $FF to SPDR
DECX ; Decrement the counter
BNE loop ; Repeat loop is counter not zero
LDA #%11111110 ; Load ACCA with last byte
JSR send_spi ; Move $FE to SPDR
RTS ; Exit subroutine
**************************************************************************************
* Routine - calibrate
* Input
- none
* Output - none
* This subroutine instructs the CS5525/6/9 to perform self-calibration.
**************************************************************************************
calibrate
LDA #$84 ; set command byte for config write
STA COMMANDBYTE ; set COMMAND BYTE
CLR HIGHBYTE ; clear HIGHBYTE
CLR MIDBYTE ; clear MIDBYTE
LDA #$01 ; get ready for self offset cal
STA LOWBYTE ; set LOWBYTE
JSR write_register ; Write to Config Register
LDA #$94 ; set command byte for config read
STA COMMANDBYTE ; set COMMAND BYTE
poll_done: JSR read_register ; Poll done flag until cal complete
BRCLR 3,LOWBYTE,poll_done; repeat if flag not set
RTS ; Exit subroutine