Originally posted by DahrkDaiz in some SMB3 doc

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BG tile animation routine: Used for action stages (not maps) for animating common objects, such as
bricks, coins, munchers, water, lava, etc.
$8E35 (0x3CE45)

$8E35:AC 1A 07 LDY $071A ; This loads the current bank from lower left corner of the pattern table
$8E38:C0 6A CPY #$6A ; 6A is the bank for the Airship, which doesn't have animated bg tiles
$8E3A:F0 21 BEQ $8E5D ; thus skip the animating routine
$8E3C:A5 15 LDA $15 ; This loads the constant timer
$8E3E:29 03 AND #$03 ; used for battleship animated tiles
$8E40: D0 1B BNE $8E5D ; but skips it on xxxx xx00 since there's only 3 frames of animation
$8E42:C8 INY
$8E43:C8 INY
$8E44:C0 76 CPY #$76 ; 74 is the last bank for the battle ship animated tile sequence (70, 72, 74)
$8E46: D0 02 BNE $8E4A ; a table isn't used here, thus, Y (from 71A) is increased twice
$8E48:A0 70 LDY #$70 ; if it reaches 76, loop back to the first animation sequence (70)
$8E4A:8C 1A 07 STY $071A ; and store it into the gfx bank
$8E4D: D0 0E BNE $8E5D
$8E4F:A5 15 LDA $15 ; this loads the constant timer and indexes it for the global
$8E51:29 18 AND #$18 ; animated tiles (coins, ? blocks, munchers, etc)
$8E53:4A LSR
$8E54:4A LSR
$8E55:4A LSR
$8E56:AA TAX
$8E57:BD FC 83 LDA $83FC,X ; Loads a bank from the animation sequence (60, 62, 64, 66)
$8E5A:8D 1A 07 STA $071A ; and finally stores it into the ram for the lower left gfx bank

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