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Routines |
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Takes the background reference from Background_Reference and executes the appropriate routine to copy the background data addresses to the buffer at Background_Data_Buffer.
Used by the routine at DrawBackground.
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Blanks the screen.
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| Change_Background | 5F22 | LD HL,$5800 | Writes 3F to all 0300 locations of the attributes buffer.
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| 5F25 | LD E,L | ||||||||||
| 5F26 | LD D,H | ||||||||||
| 5F27 | INC DE | ||||||||||
| 5F28 | LD (HL),$3F | ||||||||||
| 5F2A | LD BC,$02FF | ||||||||||
| 5F2D | LDIR | ||||||||||
| 5F2F | LD HL,$4000 | Writes 00 to all 1800 locations of the screen buffer. | |||||||||
| 5F32 | LD E,L | ||||||||||
| 5F33 | LD D,H | ||||||||||
| 5F34 | INC DE | ||||||||||
| 5F35 | LD BC,$17FF | ||||||||||
| 5F38 | LD (HL),$00 | ||||||||||
| 5F3A | LDIR | ||||||||||
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Fetch the background reference from Background_Reference and use it to calculate the address for the copy-to-buffer routine.
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| 5F3C | LD HL,$5F00 | Loads A with the contents of Background_Reference. | |||||||||
| 5F3F | LD A,(HL) | ||||||||||
| 5F40 | DEC A | Decrease it by one, then double it. | |||||||||
| 5F41 | ADD A,A | ||||||||||
| 5F42 | LD C,A | Store it as the LSB of BC (MSB is 00). | |||||||||
| 5F43 | LD B,$00 | ||||||||||
| 5F45 | LD (HL),B | Write 00 to Background_Reference. | |||||||||
| 5F46 | LD HL,$5F0A | HL=The beginning of three address references for the copy routines which populate Background_Data_Buffer at $5F0A. | |||||||||
| 5F49 | ADD HL,BC | Add BC to HL. | |||||||||
| 5F4A | LD E,(HL) | DE=One of the three background address references;
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| 5F4B | INC HL | ||||||||||
| 5F4C | LD D,(HL) | ||||||||||
| 5F4D | EX DE,HL | Swap the DE and HL registers. | |||||||||
| 5F4E | CALL Indirect_Jump | Call Indirect_Jump. | |||||||||
| 5F51 | RET | Return. | |||||||||
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Indirect jump to copy-to-buffer routine.
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| Indirect_Jump | 5F52 | JP (HL) | Indirect jump to address held by HL.
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Set up background 1.
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| 5F53 | LD HL,$602B | Copies 12 bytes of data from Background_1_Addresses to Background_Data_Buffer. | |||||||||
| 5F56 | LD DE,$5F10 | ||||||||||
| 5F59 | LD BC,$0012 | ||||||||||
| 5F5C | LDIR | ||||||||||
| 5F5E | CALL Create_Background | Call Create_Background. | |||||||||
| 5F61 | RET | Return. | |||||||||
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Set up background 2.
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| 5F62 | LD HL,$603D | Copies 12 bytes of data from Background_2_Addresses to Background_Data_Buffer. | |||||||||
| 5F65 | LD DE,$5F10 | ||||||||||
| 5F68 | LD BC,$0012 | ||||||||||
| 5F6B | LDIR | ||||||||||
| 5F6D | CALL Create_Background | Call Create_Background. | |||||||||
| 5F70 | RET | Return. | |||||||||
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Set up background 3.
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| 5F71 | LD HL,$604F | Copies 12 bytes of data from Background_3_Addresses to Background_Data_Buffer. | |||||||||
| 5F74 | LD DE,$5F10 | ||||||||||
| 5F77 | LD BC,$0012 | ||||||||||
| 5F7A | LDIR | ||||||||||
| 5F7C | CALL Create_Background | Call Create_Background. | |||||||||
| 5F7F | RET | Return. | |||||||||
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