Instruction Manual

AN88

8 AN88Rev2

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

;* Subroutines

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

;* Routine - initialize

;* Input - none

;* Output - none

;* This subroutine initializes port A 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. The

;* total delay is 555 ms upon power-up (assume uC start-up time is zero).

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

initialize CLRF PORTA ; Initialize PORTA by setting output

; data latches.

BSF STATUS, RP0 ; Select Bank 1

MOVLW 0x04 ; Value used to initialize direction

MOVWF TRISA ; Set RA2 as inputs

; RA0, RA1, RA3, & RA4 as outputs

BCF STATUS, RP0 ; Select Bank 0

BCF PORTA,SDO ; Clear SDO

MOVLW 0x32 ; Load W with delay count

CALL delay ; Delay, Power on Reset 1003 XIN

MOVLW 0xFF ; Load W with delay count

CALL delay ; Delay, Oscillator start-up 158 ms

MOVLW 0x0F ; Reset Serial Port on ADC

MOVWF TEMP

BCF PORTA,CS ; Clear CS

loop MOVLW 0xFF ; Load W with 0xFF

CALL send_spi ; Send 15 0xFF through SPI

DECFSZ TEMP,1 ; Decrement the counter

goto loop ; Repeat loop if counter not zero

MOVLW 0xFE ; Load W with last byte

CALL send_spi ; Move 0xFE to SPDR

BSF PORTA,CS ; Clear CS

RETURN ; Exit subroutine