Routines
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F1BA: Cycle a character buffer group backwards and scroll the screen left 8 columns
Used by the routines at 7866 and EC7B. Cycles one of the character buffer groups in pages 0xD7-0xDD backwards depending on the current leftmost column of the play area that is on screen (X=(7FFE)):
X Character buffer group
0, 56, 112, 168 0xD7
8, 64, 120, 176 0xD8
16, 72, 128, 184 0xD9
24, 80, 136, 192 0xDA
32, 88, 144, 200 0xDB
40, 96, 152, 208 0xDC
48, 104, 160, 216 0xDD
F1BA LD A,($7FFE) 7FFE holds X, the x-coordinate of the leftmost column of the play area on screen
F1BD SUB $38 A=0x00, 0x08, 0x10, 0x18, 0x20, 0x28 or 0x30 (depending on the value of X)
F1BF JR NC,$F1BD
F1C1 ADD A,$38
F1C3 RRCA A=0xD7-0xDD
F1C4 RRCA
F1C5 RRCA
F1C6 ADD A,$D7
F1C8 LD H,A Point HL at the first byte of the first buffer in the group
F1C9 LD L,$00
F1CB LD DE,$7F60 Copy the first buffer in the group (buffer 1) to 7F60 temporarily
F1CE LD BC,$0019
F1D1 LDIR
F1D3 LD E,B Point DE at the first byte of the first buffer in the group
F1D4 LD D,H
F1D5 LD C,$64 Move buffers 2-5 down into slots 1-4 (thus overwriting buffer 1)
F1D7 LDIR
F1D9 LD HL,$7F60 Copy buffer 1 from its temporary storage location into slot 5
F1DC LD C,$19
F1DE LDIR
F1E0 JP $E80E Scroll the screen left 8 columns (the routine at 7866 replaces this instruction with a RET)
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