|
Routines |
| Prev: 607B | Up: Map | Next: 60F9 |
|
Used by the routine at 64DC.
|
||||
| 609B | EXX | |||
| 609C | LD HL,$5801 | Point HL' and DE' at the leftmost end of the top row of attribute bytes on the screen | ||
| 609F | LD DE,$5800 | |||
| 60A2 | LD BC,$001F | We need to scroll 31 attribute bytes at a time | ||
| 60A5 | EXX | |||
| 60A6 | LD HL,$4001 | Point HL and DE at the leftmost end of the top row of pixels on the screen | ||
| 60A9 | LD DE,$4000 | |||
| 60AC | LD BC,$001F | We need to scroll 31 display file bytes at a time | ||
| 60AF | LD A,$15 | There are 21 rows of character squares to scroll | ||
| 60B1 | EX AF,AF' | |||
| 60B2 | LD A,$08 | Each row of character squares contains 8 rows of pixels | ||
| 60B4 | PUSH HL | |||
| 60B5 | PUSH DE | |||
| 60B6 | LDIR | Scroll a row of pixels left one column | ||
| 60B8 | POP DE | |||
| 60B9 | POP HL | |||
| 60BA | INC D | Point HL and DE at the next row of pixels | ||
| 60BB | INC H | |||
| 60BC | LD C,$1F | BC=001F | ||
| 60BE | DEC A | Next row in this block of 8x32 | ||
| 60BF | JR NZ,$60B4 | Jump back until this 8x32 pixel block has been scrolled | ||
| 60C1 | EXX | |||
| 60C2 | LDIR | Scroll a row of attribute bytes left one column | ||
| 60C4 | INC HL | Point HL' and DE' at the leftmost end of the next row of attribute bytes on the screen | ||
| 60C5 | INC DE | |||
| 60C6 | LD C,$1F | BC'=001F | ||
| 60C8 | EXX | |||
| 60C9 | LD A,$20 | Point HL and DE at the leftmost end of the top row of the next 8x32 block of pixels | ||
| 60CB | ADD A,E | |||
| 60CC | LD E,A | |||
| 60CD | LD A,$20 | |||
| 60CF | ADD A,L | |||
| 60D0 | LD L,A | |||
| 60D1 | EX AF,AF' | |||
| 60D2 | DEC A | Next row of character squares | ||
| 60D3 | JR Z,$60E5 | Exit this loop if all 21 rows have been scrolled left | ||
| 60D5 | CP $05 | Have we reached the bottom third of the screen? | ||
| 60D7 | JR Z,$60B1 | Jump if so | ||
| 60D9 | CP $0D | Have we reached the middle third of the screen? | ||
| 60DB | JR Z,$60B1 | Jump if so | ||
| 60DD | EX AF,AF' | |||
| 60DE | LD A,H | Point HL and DE at the leftmost end of the top row of the next 8x32 block of pixels | ||
| 60DF | SUB $08 | |||
| 60E1 | LD H,A | |||
| 60E2 | LD D,A | |||
| 60E3 | JR $60B2 | Jump back to deal with the next row of character squares | ||
|
The 21 rows of character squares have been scrolled one place to the left. Now the rightmost column needs to be filled.
|
||||
| 60E5 | EXX | |||
| 60E6 | LD HL,$581F | Point HL' and DE' at the attribute file and display file addresses for the top right of the screen, and set BC'=0020; however, these values are not used | ||
| 60E9 | LD DE,$401F | |||
| 60EC | INC C | |||
| 60ED | EXX | |||
| 60EE | LD A,($7F00) | A=leftmost column of the skool on-screen (0-64) | ||
| 60F1 | INC A | We are scrolling one column left | ||
| 60F2 | LD ($7F00),A | |||
| 60F5 | ADD A,C | A=rightmost column of the skool on-screen (31-95) | ||
| 60F6 | JP $605E | Fill in the rightmost column | ||
| Prev: 607B | Up: Map | Next: 60F9 |