; All these utility subroutines are using stack memory ; starting from FSR-1 downwards. ; Gaspar Sinai ; 2010-03-14 ;------------------------------------------------------------------------------ #include "common.inc" global FromBCD global CalculateParityAdd global CalculateParity global GetDaysInMonthBCD udata VarParity res 1 ; Parity uses this code ;------------------------------------------------------------------------------ ; Convert number in W from BCD. ; args ; W BCD ; return number ;------------------------------------------------------------------------------ FromBCD: decf FSR,F movwf INDF swapf INDF,W andlw 0FH subwf INDF,F subwf INDF,F subwf INDF,F subwf INDF,F subwf INDF,F subwf INDF,W incf FSR,F return ;------------------------------------------------------------------------------ ; Calculate parity clean ; args ; W number ; args parity(numebr) ;------------------------------------------------------------------------------ CalculateParity: clrf VarParity; the parity ;------------------------------------------------------------------------------ ;Calculate parity by adding this parity to previous parity. ; args ; W: number ; return parity(numebr) ;------------------------------------------------------------------------------ CalculateParityAdd: decf FSR,F movwf INDF CalculateParityLoop: bcf STATUS,C rrf INDF,F btfsc STATUS,C incf VarParity,F movf INDF,W btfss STATUS,Z goto CalculateParityLoop incf FSR,F movf VarParity,W return ;------------------------------------------------------------------------------ ; Get days in a month. ; args ; W MONTH (BCD) ; FSR YEARL (BCD) ; FSR+1 YEARH (BCD) ;------------------------------------------------------------------------------ GetDaysInMonthBCD: call FromBCD decf FSR,F ; save W movwf INDF addlw -.13 ; sanity check btfss STATUS,C ; skip not borrow goto GetDaysInMonthBorrow incf FSR,F ; restore stack retlw 0x31 ; ERROR GetDaysInMonthBorrow: movlw high(MonthTable) movwf PCLATH movf INDF,W ; load W incf FSR,F ; restore stack addlw low (MonthTable) btfsc STATUS,C incf PCLATH,F movwf PCL MonthTable: retlw 0x31 ; 0 ? retlw 0x31 ; JAN goto GetDaysInMonthFeb retlw 0x31 ; MAR retlw 0x30 ; APR retlw 0x31 ; MAY retlw 0x30 ; JUN retlw 0x31 ; JUL retlw 0x31 ; AUG retlw 0x30 ; SEP retlw 0x31 ; OCT retlw 0x30 ; NOV retlw 0x31 ; DEC ; ; args ; FSR YEARL (BCD) ; FSR+1 YEARH (BCD) ; return number of days in february (BCD) ; GetDaysInMonthFeb: movf INDF,W ; load year BCD low btfsc STATUS,Z goto GetDaysInMonthFeb100 call FromBCD andlw 3 btfss STATUS,Z retlw 0x28 ; every year except 4 retlw 0x29 ; every 4 years GetDaysInMonthFeb100: ; every 100 years incf FSR,F movf INDF,W ; load year BCD high decf FSR,F call FromBCD andlw 3 btfss STATUS,Z retlw 0x28 ; every 100 years except 400 retlw 0x29 ; every 400 years end