; TOLOWER:

;

; Convert a null-terminated character string to all lower case.

; Maximum string length is 255 characters, plus the null term-

; inator.

;

; Parameters:

;

; SRC - Source string address

; DST - Destination string address

;

        ORG
 $0080

;

0080
 00
 04
 SRC
 .WORD
 $0400
 ;source string pointer ($40)

0082
 00
 05
 DST
 .WORD
 $0500
 ;destination string pointer ($42)

;

0600
 ORG
 $0600
 ;execution start address

;

0600
 A0
 00
 TOLOWER
 LDY
 #
$00
 ;starting index

;

0602
 B1
 80
 LOOP
 LDA
 (
SRC
),
Y
 ;get from source string

0604
 F0
 11
 BEQ
 DONE
 ;end of string

;

0606
 C9
 41
 CMP
 #
'A'
 ;if lower than UC alphabet...

0608
 90
 06
 BCC
 SKIP
 ;copy unchanged

;

060
A
 C9
 5
B
 CMP
 #
'Z'
+
1
 ;if greater than UC alphabet...

060
C
 B0
 02
 BCS
 SKIP
 ;copy unchanged

;

060
E
 09
 20
 ORA
 #
%00100000
 ;convert to lower case

;

0610
 91
 82
 SKIP
 STA
 (
DST
),
Y
 ;store to destination string

0612
 C8
 INY
 ;bump index

0613
 D0
 ED
 BNE
 LOOP
 ;next character

;

; NOTE: If .Y wraps the destination string will be left in an undefined

; state. We set carry to indicate this to the calling function.

;

0615
 38
 SEC
 ;report string too long error &...

0616
 60
 RTS
 ;return to caller

;

0617
 91
 82
 DONE
 STA
 (
DST
),
Y
 ;terminate destination string

0618
 18
 CLC
 ;report conversion completed &...

0619
 60
 RTS
 ;return to caller

;

                       .END