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$91E8: Move sprites #0-#6 left by 64 pixels (2)
Used by the routine at $98E8.
Input
X Bit 8 of the sprites' x-coordinates
$91E8 LDY #$0E Bits 0-7 of the x-coordinate of sprite #7 is at $D00E.
$91EA TXA Compensate for the TAX instruction coming next.
This entry point is used by the routine at $92E8.
$91EB TAX Transfer bit 8 of the sprites' x-coordinates to X.
$91EC DEY Decrease Y by 2 to point at bits 0-7 of the x-coordinate of the next sprite.
$91ED DEY
$91EE BPL $91F6 Branch if Y is still non-negative.
$91F0 STX $D010 Update bit 8 of the sprites' x-coordinates.
$91F3 JMP $9877 Enable sprites #0-#6.
$91F6 STY $92E9 Modify the LSB of the operand of the 'LDA nnnn' instruction at $92E8.
$91F9 STY $92EF Modify the LSB of the operand of the 'STA nnnn' instruction at $92EE.
$91FC JMP $92E8 Continue at $92E8.
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