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re-arrange readme
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Bernd Boeckmann
146
README.md
146
README.md
@@ -14,72 +14,41 @@ assembly are not supported. This may be implemented in the future.
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## Example
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The following example implements a hello world program for the Commodore C64.
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Assemble with `asm6502 helloc64.asm helloc64.prg`.
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Assemble with `asm6502 helloc64.asm helloc64.prg helloc64.lst` to generate
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`helloc64.prg` containing the C64 program and `helloc64.lst` containing
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the program listing.
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; C64 Hello World
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; assemble to .PRG file: asm6502 helloc64.asm helloc64.prg
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; assemble to .PRG file: asm6502 helloc64.asm helloc64.prg helloc64.lst
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LOAD_ADDR = $0801
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.word LOAD_ADDR ; .PRG header: load address
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.org LOAD_ADDR
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.word LOAD_ADDR ; .PRG header: load address
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.org LOAD_ADDR
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CHROUT = $FFD2 ; kernal function address
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SYS = $9E ; basic SYS token number
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CR = 13 ; carrige return character
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LF = %1010 ; line feed character
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basic_upstart: ; BASIC code: 10 SYS 2062
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.word @end, 10 ; ptr to next basic line and line number 10
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.byte SYS, " 2062", 0 ; SYS token and address string of subroutine
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.word @end, 10 ; ptr to next basic line and line number 10
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.byte SYS, " 2062",0 ; SYS token and address string of subroutine
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@end .word 0 ; null ptr to indicate end of basic text
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start: ; this is at address 2062 ($080E)
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ldx #0
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@l lda hello_msg,x
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jsr CHROUT
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inx
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cpx #hello_len
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bne @l
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rts
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ldx #0
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@l lda hello@msg,x
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jsr CHROUT
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inx
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cpx #hello@len
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bne @l
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rts
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hello_msg .byte "HELLO, WORLD!", CR, LF
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hello_len = @ - hello_msg
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To produce a listing file assemble with
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`asm6502 helloc64.asm helloc64.prg hello64.lst`. The output looks like this:
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ASM6502 LISTING FOR helloc64.asm @ 2023-04-02 17:27
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FPos PC Code Line# Assembler text
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1: ; C64 Hello World
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2: ; assemble to .PRG file: asm6502 helloc64.asm helloc64.prg
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3:
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4: LOAD_ADDR = $0801
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5:
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0000 0000 01 08 6: .word LOAD_ADDR ; .PRG header: load address
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7: .org LOAD_ADDR
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8:
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9: CHROUT = $FFD2 ; kernal function address
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10: SYS = $9E ; basic SYS token number
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11: CR = 13 ; carrige return character
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12: LF = %1010 ; line feed character
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13:
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14: basic_upstart: ; BASIC code: 10 SYS 2062
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0002 0801 0C 08 0A 15: .word @end, 10 ; ptr to next basic line and line number 10
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0006 0805 9E 20 32 ... 16: .byte SYS, " 2062",0 ; SYS token and address string of subroutine
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000D 080C 00 00 17: @end .word 0 ; null ptr to indicate end of basic text
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18:
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19: start: ; this is at address 2062 ($080E)
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000F 080E A2 00 20: ldx #0
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0011 0810 BD 1C 08 21: @l lda hello_msg,x
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...
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The column *FPos* indicates the position in the output file while *PC*
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indicates the address of the program counter. FPos and PC may not be in sync
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if an *.ORG* directive is used in the assembler text. It may be used if the
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binary image is not loaded to address zero, for example if it is loaded as
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a .PRG file on commodore systems.
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hello:
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@msg .byte "HELLO, WORLD!", CR, LF
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@len = @ - @msg
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CR = 13 ; carrige return character
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LF = %1010 ; line feed character as binary number
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## Constraints
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```
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@@ -324,3 +293,76 @@ This one is correct (indirect addressing):
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ORA (15,x)
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ORA (15),y
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## Listing Files
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ASM6502 is capable of producing listing files containing the generated
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code in hexedecimal representation along the lines of the input file. It also
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contains a list of global labels and variables once sorted by address and once
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sorted by name
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The column *FPos* indicates the position in the output file while *PC*
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indicates the address of the program counter. FPos and PC may not be in sync
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if an *.ORG* directive is used in the assembler text.
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Listing of the `helloc64.asm` file from the introduction:
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ASM6502 LISTING FOR helloc64.asm @ 2023-04-09 14:19
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FPos PC Code Line# Assembler text
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1: ; C64 Hello World
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2: ; assemble to .PRG file: asm6502 helloc64.asm helloc64.prg
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3:
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4: LOAD_ADDR = $0801
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5:
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0000 0000 01 08 6: .word LOAD_ADDR ; .PRG header: load address
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7: .org LOAD_ADDR
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8:
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9: CHROUT = $FFD2 ; kernal function address
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10: SYS = $9E ; basic SYS token number
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11:
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12: basic_upstart: ; BASIC code: 10 SYS 2062
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0002 0801 0C 08 0A 13: .word @end, 10 ; ptr to next basic line and line number 10
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0006 0805 9E 20 32 ... 14: .byte SYS, " 2062",0 ; SYS token and address string of subroutine
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000D 080C 00 00 15: @end .word 0 ; null ptr to indicate end of basic text
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16:
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17: start: ; this is at address 2062 ($080E)
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000F 080E A2 00 18: ldx #0
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0011 0810 BD 1C 08 19: @l lda hello@msg,x
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0014 0813 20 D2 FF 20: jsr CHROUT
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0017 0816 E8 21: inx
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0018 0817 E0 0F 22: cpx #hello@len
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001A 0819 D0 F5 23: bne @l
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001C 081B 60 24: rts
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25:
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26: hello:
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001D 081C 48 45 4C ... 27: @msg .byte "HELLO, WORLD!", CR, LF
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28: @len = @ - @msg
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29:
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30: CR = 13 ; carrige return character
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31: LF = %1010 ; line feed character (decimal 10)
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<<< SYMBOLS BY NAME >>>
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HEX DEC NAME
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V FFD2 65490 CHROUT
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V 000D 13 CR
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V 000A 10 LF
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V 0801 2049 LOAD_ADDR
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V 9E 158 SYS
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L 0801 2049 basic_upstart
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L 081C 2076 hello
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L 080E 2062 start
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<<< SYMBOLS BY VALUE >>>
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HEX DEC NAME
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V 000A 10 LF
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V 000D 13 CR
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V 9E 158 SYS
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L 0801 2049 basic_upstart
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V 0801 2049 LOAD_ADDR
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L 080E 2062 start
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L 081C 2076 hello
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V FFD2 65490 CHROUT
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