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SCHG How-to

Relocate Player Object Logic in Sonic 2 SMS

From Sonic Retro

(Original guide by Glitch)

Introduction

This guide will show you how to increase the the Sonic 2 ROM from 32 to 64 banks and move the logic for the Sonic object into bank 32. This gives you much more room to breathe when editing the player object not to mention extra space for art!

Increasing the ROM Size

We're going to start by increasing the ROM size. Open src/s2.asm and find the section that starts ".ROMBANKMAP". It should look like this:

.ROMBANKMAP
BANKSTOTAL 32
BANKSIZE $7FF0
BANKS 1
BANKSIZE $0010
BANKS 1
BANKSIZE $4000
BANKS 30
.ENDRO

Change it to look like this:

.ROMBANKMAP
BANKSTOTAL 64
BANKSIZE $7FF0
BANKS 1
BANKSIZE $0010
BANKS 1
BANKSIZE $4000
BANKS 62
.ENDRO

That was easy enough...

Prepare the Source Files

Now we're going to add a source file for the 32nd bank. Create a new file called "bank32.asm" in the src/includes dir. Open the src/includes/banks.asm file. Add the following lines at the end and save:

.BANK 32
.ORG $0000
Bank32:

.include "src\includes\bank32.asm"

Move the Logic

Open src/object_logic/bank31_logic.asm. It should start with the following lines:

.include "src\object_logic\logic_sonic.asm"

.include "src\object_logic\logic_ring_sparkle.asm"

.include "src\object_logic\logic_block_fragment.asm"

Cut the line that includes the logic for the Sonic object and paste it into the "bank32.asm" file. Save everything and build the ROM.