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-       BASELINE 2091 Presents The First Guide To Coding The SNES
-                    Guide and Source Code by -Pan-
-                         Released on 4/20/93
-
-
-       Welcome to the first installment of "How to code SNES"
- This first volume will show you how to make a simple text intro. It uses
-mode 0 graphics with no DMAs (Horizontal or General) and is the simplest
-type of intro you can make. We're starting small so you can easily understand
-what to do. Other future volumes will contain other graphic modes,
-Horizontal DMA (HDMA, the SNES version of an amiga copperlist), General DMA,
-Interrupts, and a brief section on Sound. Originally we were going to release
-the full Super Famicom Programmer's Manual but believe it or not, this manual
-a pile of garbage. Contrary to the popular belief that we always had the
-manual, this is NOT true. The White Knight happened to meet a very cool
-guy at the CEBIT in Germany and has gotten the manual 2 weeks ago!
-Yes! What you have seen from us before was true coding. We started out
-by hacking and working our way to the top. We didn't wait until we bought
-a manual. In fact, the manual was sent to us for FREE! This book isn't
-worth paying for!
- 
-Let's clear up a few misunderstandings about that SNES manual!
- 
-1) This book does NOT teach you assembly language!!
-   It would help if you knew a little before trying to code this machine!
-
-2) This book was not written such as other reference guides you can find in
-   a store, like Mapping the Amiga, or even Mapping the C64.
-   It tells you barely and confusingly what the registers do. Period.
-
-3) This book is about 148 pages long and that includes the Sound Section.
-   Some have said it was the size of a phone book. Unless live in
-   Mud Hole, Kentucky this is NOT the case!
- 
-
-So much for the introduction. I personally feel that experience is better
-than a reference guide. Reading a text file does not give you the feel of the
-machine. In the included source file, you will notice that almost every line
-has a description of what it is doing. This is better than telling you the
-registers and letting you fiddle around. You know what it will do, and you
-can see it in action in the assembled output (also included). I suggest
-you examine the source code right after reading this brief introduction on
-how the SNES system operates.
- 
-The SNES runs on a 65816 processor. This is similar to the 6502, but many
-new instructions are available. You will use the most popular commands
-like LDA, LDX, STA, PHA, PLA, RTS, JMP.. etc etc.   There are some new
-ones but we will get into that subject in the next volume as it is not
-very important right now.
-The 65816 is a 16 bit processor that does 24 bit addressing.
-You can load and store 16 bit numbers, as well as 8 bit. The addressing is
-is different than the 6502 in that it includes a bank. If you have coded on
-the C64 you know that the addressing on the C64 was from $0000-$FFFF.
-That is 16 bit addressing. 24 bit includes 1 extra byte. This one byte
-is the BANK number.  The SNES memory is broken down into fragments of
-32k blocks each. They are addressed from $8000-$FFFF and are stored into
-banks sequentially. If you wanted to access the first ROM byte in memory, 
-the address would be $008000. The first $00 is the bank number, the first
-bank you can access. The $8000 is the 16 bit address. All banks (unless in
-high rom 64k bank memory) start at $8000!
-Remember that you can not write ROM. If you have coded on a C64 you have
-written a routine that looked like this:
-
-lda #$00
-sta $c000
- 
-You cannot do this! $c000 is ROM and you can not write to ROM!
-To write to ram, simply write to any address between $0000-$1fff.
-If you need more memory you will find plenty at bank $7e and $7f
-These 2 banks contain memory from $0000-$ffff. These 2 banks each contain
-64k ofram totalling 128k for your own use!
-If you need to write to these directly, just use the LONG STA command
-example:
-sta $7ec000
- 
-This will write to bank $7e at address $c000!
-
-Fair enough. This was only a brief lecture on how the memory works.
-
- 
-The SNES hardware registers and how the work:
-
-You will notice when looking at the source code something very strange.
-Some registers are written to twice in a row! This because some registers
-need more than one 8 bit info, such as the scroll X registers. In these
-registers you can enter any number between $0-$07ff, but they are written
-as two 8 bit numbers, one right after another.
-example:
- 
-lda #$07
-sta $210d
-lda #$00
-sta $210d
- 
-This writes #$0007 to $210d, plane 0 scroll x register.
-
-Using 16 bit data storage will not work for this type of register!
-example:
-
-lda #$0007
-sta $210d
-
-This will not work because it will write #$07 to $210d, then a #$00 to $210e.
-
-Another strange register is the self-incrementing register such as the VRAM
-address registers $2116 and $2117.
-After writing to $2119 (or $2118 in another setting) the VRAM address in
-$2116 and $2117 will be increased. You do not have to do it yourself.
-This can be seen in the Character set (font set) transfer  routine in the 
-source code.
-
- 
-Introduction to Video RAM (VRAM)
- 
-The Super NES system has it own graphics processor. This requires its own
-ram to read/write graphics data.  This ram can only be accessed through
-certain registers such as $2118 + $2119.  To access Video Ram you MUST
-turn off the video or you must be in screen blank (horizontal or vertical).
-This is one of the downsides of the SNES.
-Video Ram allows the storage of map planes and tile graphics.
-VRAM is only 64k long and can not be used as regular ram. You can not
-program in it, it is a separate unit!
-
-In this volume we show you how to make a text screen in Mode 0. There are
-8 graphic modes numbered from Mode 0 to Mode 7.   Mode 0 is the most 
-simplistic. It allows only 4 colors per tile, but allows all four 
-planes to be used.
- 
-A normal video screen on the SNES is 32*32 tiles, which comes out to an
-even 1024 tiles. You can widen the screen but you still may only have
-1024 tiles. There are 2 parts to displaying a graphic on the screen.
-There is the tile graphic data which gives the tile its picture. Then there
-is the Map data. These are individually placed tiles placed on the screen
-to produce an image.
-
-example:
-
-                BBBBB   SSSSS  LL
-                BB  BB SS      LL
-                BBBBB   SSSS   LL
-                BB  BB     SS  LL
-                BBBBB  SSSSS   LLLLLLL
-
-Notice that all the small B's are the same. These woulds be drawn as
-Tile Graphics. They all form together to create the large B image.
-These B's together would be the Map data. The same would go for the S and L.
-
-This is enough info to understand the basics of this 2 color intro.
-This next installment on "How to code SNES" will feature more interesting
-subjects as:
- 
- - How the color works
- - 16 color graphic mode
- - the entire 65816 instruction set with op-codes
- - more info on the joypad
-