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The gameboy permanently compares the value of the LYC and LY registers. The values between 144 and 153 indicate the V-Blank period. The LY can take on any value between 0 through 153. The LY indicates the vertical line to which the present data is transferred to the LCD Driver. Values in range from 0-255 may be used for X/Y each, the video controller automatically wraps back to the upper (left) position in BG map when drawing exceeds the lower (right) border of the BG map area. Specifies the position in the 256x256 pixels BG map (32x32 tiles) which is to be displayed at the upper/left LCD display position. LCD Position and Scrolling FF42 - SCY - Scroll Y (R/W) FF43 - SCX - Scroll X (R/W) This can be useful for dynamically controlling the SCX/SCY registers ($FF43/$FF42) to perform special video effects. One very popular reason is to indicate to the user when the video hardware is about to redraw a given LCD line. There are various reasons for this interrupt to occur as described by the STAT register ($FF40). This period lasts approximately 1.1 milliseconds. This interrupt occurs at the beginning of the V-Blank period (LY=144).ĭuring this period video hardware is not using video ram so it may be freely accessed. ![]() 59.7 times a second on a regular GB and ca. A complete screen refresh occurs every 70224 clks.) LCD Interrupts INT 40 - V-Blank Interrupt A complete cycle through these states takes 456 clks. Mode 0 is present between 201-207 clks, 2 about 77-83 clks, and 3 about 169-175 clks. The mode flag stays set at 1 for about 1.08 ms. This is interrupted every 16.6ms by the VBlank (1). 0 is present about 48.6 µs, 2 about 19 µs, and 3 about 41 µs. ![]() The Mode Flag goes through the values 0, 2, and 3 at a cycle of about 109 µs. LCD Control Register FF40 - LCDC - LCD Control (R/W) For specific information read the chapter about Memory Bank Controllers. External memory is often battery buffered, and may hold saved game positions and high scrore tables (etc.) even when the gameboy is turned of, or when the cartridge is removed. The second area is often used to address external RAM, or to address other external hardware (Real Time Clock, etc). The first area is typically used to address ROM (read only, of course), cartridges with Memory Bank Controllers (MBCs) are additionally using this area to output data (write only) to the MBC chip. ![]() The areas from 0000-7FFF and A000-BFFF may be used to connect external hardware. For more information read the chapter about The Cartridge Header. Most of the bytes in this area are required to be specified correctly. This area contains information about the program, its entry point, checksums, information about the used MBC chip, the ROM and RAM sizes, etc. The memory at 0100-014F contains the cartridge header. RST commands are 1-byte opcodes that work similiar to CALL opcodes, except that the destination address is fixed. However, the memory may be used for any other purpose in case that your program doesn’t use any (or only some) RST commands or Interrupts. #Gameboy dmg cpu internals mod#However, it is important to note that this mod is NOT compatible with actual Game Boy Advance cables (unless you modify them).0000,0008,0010,0018,0020,0028,0030,0038 for RST commands The GBA connector is fully backwards-compatible with the smaller-style port used in the Game Boy Color and Game Boy Pocket, as well as the official Super Game Boy 2. This mod board uses a GBA-style port because it is still possible to purchase them new without cannibalizing a Game Boy console just for this one connector. įirst of all, you can purchase this mod board on my Tindie store: The mod board comes with all of the necessary components pre-installed, as well as a pair of nylon standoffs to help securely mount the board in the cart shell. #Gameboy dmg cpu internals install#Note that in order for this mod to work properly, you will also need to install the Super Game Boy Clock Mod. #Gameboy dmg cpu internals how to#If you have a steady hand and good equipment, here's how to go about doing it. It is possible to install one, but it requires fine-pitch soldering directly to several pins on the DMG CPU. ![]() In addition to the clock speed issue, the Super Game Boy did not include a link port for multiplayer connectivity. ![]()
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