Updated

OperatingSystem/monitor_v2/include/conversions.s

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+; HL Contains Address to string
+; E is 0xFF if error
+; E is 0x00 if okay
+; A returns byte
+; A,DE are destroyed
+DHEX_TO_BYTE:
+    PUSH HL             ;Backup pointer
+    ; Load First Byte
+    LD A,(HL)           ;Load first char (high)
+    CALL HEX_TO_BIN     ;Conv chart to 4bit
+    jr C, DHEX_TO_BYTE_FAILED   ;If error jmp to DHEX_TO_BYTE_FAILED
+    SLA A               ;shift result to upper 4 bits
+    SLA A
+    SLA A
+    SLA A
+    LD D,A              ;store result in D
+
+    INC HL              ;next byte
+    LD A,(HL)           ;load 2nd char (lower)
+    CALL HEX_TO_BIN     ;Conv chart to 4bit
+    jr C, DHEX_TO_BYTE_FAILED   ;If error jmp to DHEX_TO_BYTE_FAILED
+    OR D                ;merge D with accumulator
+
+    POP HL              ;restor original pointer
+    LD E,0x00           ;set error to 0x00 = no error
+    RET
+DHEX_TO_BYTE_FAILED:
+    LD E,0xFF           ;set error to oxFF
+    ;LD A,0x00
+    POP HL
+    RET
+
+; REG A Contains CHAR-Low
+; If failed, Carry is set
+HEX_TO_BIN:
+    SUB 48 ; 0 is 0
+    jp PE, HEX_TO_INVALID_2; to low (SUB overflow)
+    CP 10 ; Value is between 0 and 9
+    JR C, HEX_TO_BIN_2
+    SUB 7
+    jp PE, HEX_TO_INVALID_2; to low (SUB overflow)
+HEX_TO_BIN_2:
+    CP 16
+    JR NC, HEX_TO_INVALID_2; if bigger than 15-> fail
+    AND 0x0F
+    RET
+HEX_TO_INVALID_2:
+    SCF ;set carry flag
+    RET
+
+
+;*****************
+; Convert Byte to Hex Char (ASCII)
+;*****************
+;Description: the StrLength function inline
+;
+;Inputs: A contains input byte
+;
+;Outputs: BC contains 2 Bytes of ASCII (HEX)
+;
+;Destroys: A, BC,
+STRCONV_BYTES_TO_HEX:
+    PUSH AF;Backup A Register
+    RRA
+    RRA
+    RRA
+    RRA
+    CALL STRCONV_BYTES_TO_HEX_1
+    ;LD A,D
+    LD B,A  
+    POP AF ; Reload first Byte
+    CALL STRCONV_BYTES_TO_HEX_1
+    ;LD A,D
+    LD C,A
+    RET
+
+STRCONV_BYTES_TO_HEX_1:
+    AND 0x0F
+    ADD 48
+    CP 58 ; Check if less than 58 (less than ASCII 9)
+    ;JR C, STRCONV_BYTES_TO_HEX_2
+    RET C
+    ADD 7 ; A-F
+    RET
+STRCONV_BYTES_TO_HEX_2:
+    ;LD D,A
+    RET
+
+