;export symbols
	XDEF  PulseWidthMod	
	XREF	__SEG_END_SSTACK,TON,TOFF,PRESSED,PORT_T,FourMSDelay,Keypad
	
	
PulseWidthMod:
            PSHA                ;preserve registers
            PSHB
            PSHX
            PSHY

PulseWidthMain:            
            JSR     Keypad      ;call Keypad subroutine
            LDAA    PRESSED     ;load the pressed value ;7.1 ?
            CMPA    #$00        ;check if no value has been pressed ;7.1 ?
            ; use previous value for TON and TOFF ?
            BEQ     Return      ;go back to the calling routine
            
CheckTON:
            LDAB    TON         ;load TON to check if TON is zero
            CMPB    #$00        ;conditional if TON is zero
            ;BEQ     CheckTOFF  ;check TOFFF if TON is zero
            BNE     SetTAndDelay;following instructions? ;7.1 ?
            
CheckTOFF:                      ;will be called if TON is equal to zero
            LDAB    TOFF        ;load TOFF into Acc. B
            CMPB    #$00        ;check if TOFF == #$00
            BEQ     PulseWidthMain ;"branch back to the keypad routine" ? should this be BEQ Keypad ?

SetTAndDelay:
            BSET    PORT_T,#%00001000 ;set bit 3 of Port T
            JSR     FourMSDelay       ;delay 4 ms
            LDAA    TON               ;load TON into Acc. A
            DECA                      ;decrement A
            STAA    TON               ;now we have decremented TON by way of Acc. A0
            BRA     CheckTON          ;check TON again
            
ClearTAndDelay:
            BCLR    PORT_T,#%00001000 ;clear bit 3 of Port T
            JSR     FourMSDelay       ;delay 4 ms
            LDAA    TOFF              ;load TOFF into Acc. A
            DECA                      ;decrement A
            STAA    TOFF              ;TOFF has been effectively decremented
            BRA     CheckTOFF         ;check TOFF again after decrementation
            
Return:
            PULY                ;restore the registers
            PULX
            PULB
            PULA
            
            RTI