TempOnes:		.rs 2
TempTens:		.rs 2
TempHund:		.rs 2
TempThous:		.rs 2
TempTenThous:	.rs 2

;for example, let's use the following decimal numbers to convert to 16-bit binary
;13,268

Math:
  LDX #$00
  LDA #$08	;ones digit. You'd use $0201 for this or whatever the ones digit is in the code
  ASL A 	;x2 to get to the hi byte of the correct digit
  LDA OnesDigit,x
  STA TempOnes
  INX
  LDA OnesDigit,x
  STA TempOnes+1

  LDX #$00
  LDA #$06
  ASL A
  LDA TensDigit,x
  STA TempTens
  INX
  LDA TensDigit,x
  STA TempTens+1

  LDX #$00
  LDA #$02
  ASL A
  LDA HundredsDigit,x
  STA TempHund
  INX
  LDA HundredsDigit,x
  STA TempHund+1

  LDX #$00
  LDA #$03
  ASL A
  LDA ThousandsDigit,x
  STA TempThous
  INX
  LDA ThousandsDigit,x
  STA TempThous+1

  LDX #$00
  LDA #$01
  ASL A
  LDA TenThousandsDigit,x
  STA TempTenThous
  INX
  LDA TenThousandsDigit,x
  STA TempTenThous+1

;;setup math is done

  LDA TempOnes+1 	;starting to add the bytes together, one digit at a time
  CLC				;this is ones+tens
  ADC TempTens+1
  STA TempOnes+1 	;this will be our recurring lowbyte addition value
  LDA TempOnes
  ADC TempTens
  STA TempOnes		;this will be our recurring hibyte addition value

  LDA TempOnes+1 	;this is ones+tens solution+hundreds
  CLC
  ADC TempHund+1
  STA TempOnes+1
  LDA TempOnes
  ADC TempHund
  STA TempOnes

  LDA TempOnes+1 	;previous solution+thousands
  CLC
  ADC TempThous+1
  STA TempOnes+1
  LDA TempOnes
  ADC TempThous
  STA TempOnes

  LDA TempOnes+1 	;previous solution+ten thousands
  CLC
  ADC TempTenThous+1
  STA TempOnes+1 		;TempOnes+1 is now your final low byte
  LDA TempOnes
  ADC TempTenThous
  STA TempOnes			;TempOnes is now your final hi byte
  RTS

OnesDigit:
  .db $00,$00	;0
  .db $00,$01	;1
  .db $00,$02	;2
  .db $00,$03	;3
  .db $00,$04	;4
  .db $00,$05	;5
  .db $00,$06	;6
  .db $00,$07	;7
  .db $00,$08	;8
  .db $00,$09	;9

TensDigit:
  .db $00,$00 	;00
  .db $00,$0A	;10
  .db $00,$14	;20
  .db $00,$1E	;30
  .db $00,$28	;40
  .db $00,$32	;50
  .db $00,$3C	;60
  .db $00,$46	;70
  .db $00,$50	;80
  .db $00,$5A	;90

 HundredsDigit:
  .db $00,$00	;000
  .db $00,$64	;100
  .db $00,$C8	;200
  .db $01,$2C	;300
  .db $01,$90	;400
  .db $01,$F4	;500
  .db $02,$58	;600
  .db $02,$BC	;700
  .db $03,$20	;800
  .db $03,$84	;900

 ThousandsDigit:
  .db $00,$00 	;0000
  .db $03,$E8	;1000
  .db $07,$D0	;2000
  .db $0B,$B8	;3000
  .db $0F,$A0	;4000
  .db $13,$88	;5000
  .db $17,$70	;6000
  .db $1B,$58	;7000
  .db $1F,$40	;8000
  .db $23,$28	;9000

 TenThousandsDigit:
  .db $00,$00 	;00000
  .db $27,$10 	;10000
  .db $4E,$20 	;20000
  .db $75,$30	;30000
  .db $9C,$40 	;40000
  .db $C3,$50 	;50000
  .db $EA,$60 	;60000	;this is as high as you can go for 16-bit math