| C64 ROM | Routines |
| Prev: A38A | Up: Map | Next: A3FB |
| A3B8 | 20 08 A4 | JSR $A408 | check available memory, do out of memory error if no room | |
| A3BB | 85 31 | STA $31 | set end of arrays low byte | |
| A3BD | 84 32 | STY $32 | set end of arrays high byte | |
|
This entry point is used by the routine at B526.
open up a space in the memory, don't set the array end
|
||||
| A3BF | 38 | SEC | set carry for subtract | |
| A3C0 | A5 5A | LDA $5A | get block end low byte | |
| A3C2 | E5 5F | SBC $5F | subtract block start low byte | |
| A3C4 | 85 22 | STA $22 | save MOD(block length/$100) byte | |
| A3C6 | A8 | TAY | copy MOD(block length/$100) byte to Y | |
| A3C7 | A5 5B | LDA $5B | get block end high byte | |
| A3C9 | E5 60 | SBC $60 | subtract block start high byte | |
| A3CB | AA | TAX | copy block length high byte to X | |
| A3CC | E8 | INX | +1 to allow for count=0 exit | |
| A3CD | 98 | TYA | copy block length low byte to A | |
| A3CE | F0 23 | BEQ $A3F3 | branch if length low byte=0 | |
|
block is (X-1)*256+Y bytes, do the Y bytes first
|
||||
| A3D0 | A5 5A | LDA $5A | get block end low byte | |
| A3D2 | 38 | SEC | set carry for subtract | |
| A3D3 | E5 22 | SBC $22 | subtract MOD(block length/$100) byte | |
| A3D5 | 85 5A | STA $5A | save corrected old block end low byte | |
| A3D7 | B0 03 | BCS $A3DC | branch if no underflow | |
| A3D9 | C6 5B | DEC $5B | else decrement block end high byte | |
| A3DB | 38 | SEC | set carry for subtract | |
| A3DC | A5 58 | LDA $58 | get destination end low byte | |
| A3DE | E5 22 | SBC $22 | subtract MOD(block length/$100) byte | |
| A3E0 | 85 58 | STA $58 | save modified new block end low byte | |
| A3E2 | B0 08 | BCS $A3EC | branch if no underflow | |
| A3E4 | C6 59 | DEC $59 | else decrement block end high byte | |
| A3E6 | 90 04 | BCC $A3EC | branch always | |
| A3E8 | B1 5A | LDA ($5A),Y | get byte from source | |
| A3EA | 91 58 | STA ($58),Y | copy byte to destination | |
| A3EC | 88 | DEY | decrement index | |
| A3ED | D0 F9 | BNE $A3E8 | loop until Y=0 | |
|
now do Y=0 indexed byte
|
||||
| A3EF | B1 5A | LDA ($5A),Y | get byte from source | |
| A3F1 | 91 58 | STA ($58),Y | save byte to destination | |
| A3F3 | C6 5B | DEC $5B | decrement source pointer high byte | |
| A3F5 | C6 59 | DEC $59 | decrement destination pointer high byte | |
| A3F7 | CA | DEX | decrement block count | |
| A3F8 | D0 F2 | BNE $A3EC | loop until count = $0 | |
| A3FA | 60 | RTS | ||
| Prev: A38A | Up: Map | Next: A3FB |