The Motorola MC68000 microprocessor is the CPU used in the A1000, the A500, and the A2000. The 68000 is a 16/32-bit microprocessor; internal registers are 32 bits wide, while the data bus and ALU are 16 bits. The 68000's system clock speed is 7.15909 MHz on NTSC systems (USA) or 7.09379 MHz on PAL systems (Europe). These speeds can vary when using an external system clock, such as from a genlock board. The 68000 has an address space of 16 megabytes. In the Amiga, the 68000 can address up to 9 megabytes of random access memory (RAM). In the A3000, the Motorola MC68030 microprocessor is the CPU. This is a full 32-bit microprocessor with a system clock speed of 16 or 25 megahertz. The 68030 has an address space of 4 gigabytes. In the A3000, over a gigabyte of RAM can be addressed. In addition to the 680x0, all Amiga models contain special purpose hardware known as the custom chips that greatly enhance system performance. The term custom chips refers to the three integrated circuits which were designed specifically for the Amiga computer. These three custom chips, named Paula, Agnus, and Denise, each contain the logic to handle a specific set of tasks such as video, audio, or I/O. Because the custom chips have DMA capability, they can access memory without using the 680x0 CPU - this frees the CPU for other types of operations. The division of labor between the custom chips and the 680x0 gives the Amiga its power; on most other systems the CPU has to do everything. The memory shared between the Amiga's CPU and the custom chips is called Chip memory. The more Chip memory the Amiga has, the more graphics, audio, and I/O data it can operate on without the CPU being involved. All Amigas can access at least 512K of Chip memory. The latest version of the custom chips, known as the Enhanced Chip Set or ECS, can handle up to 2 MB of memory and has other advanced features. For more details about the Enhanced Chip Set, refer to Appendix C . Although there are different versions of the Amiga's custom chips, all versions have some common features. Among other functions, the custom chips provide the following: * Bitplane generated, high resolution graphics capable of supporting both PAL and NTSC video standards. NTSC systems. ------------- On NTSC systems, the Amiga typically produces a 320 by 200 non-interlaced or 320 by 400 interlaced display in 32 colors. A high resolution mode provides a 640 by 200 non-interlaced or 640 by 400 interlaced display in 16 colors. PAL systems. ------------ On PAL systems, the Amiga typically produces a 320 by 256 non-interlaced or 320 by 512 interlaced display in 32 colors. High resolution mode provides a 640 by 256 non-interlaced or 640 by 512 interlaced display in 16 colors. The design of the Amiga's display system is very flexible and there are many other modes available. Hold-and-modify (HAM) mode allows for the display of up to 4,096 colors on screen simultaneously. Overscan mode allows the creation of higher resolution displays specially suited for video and film applications. Displays of arbitrary size, larger than the visible viewing area can be created. Amigas which contain the Enhanced Chip Set (ECS) support Productivity mode giving displays of 640 by 480, non-interlaced with 4 colors from a pallette of 64. * A custom graphics coprocessor, called the Copper, that allows changes to most of the special purpose registers in synchronization with the position of the video beam. This allows such special effects as mid-screen changes to the color palette, splitting the screen into multiple horizontal slices each having different video resolutions and color depths, beam-synchronized interrupt generation for the 680x0, and more. The coprocessor can trigger many times per screen, in the middle of lines, and at the beginning or during the blanking interval. The coprocessor itself can directly affect most of the registers in the other custom chips, freeing the 680x0 for general computing tasks. * 32 system color registers, each of which contains a 12-bit number as four bits of red, four bits of green, and four bits of blue intensity information. This allows a system color palette of 4,096 different choices of color for each register. * Eight reusable 16-bit wide sprites with up to 15 color choices per sprite pixel (when sprites are paired). A sprite is an easily movable graphics object whose display is entirely independent of the background (called a playfield); sprites can be displayed over or under this background. A sprite is 16 low resolution pixels wide and an arbitrary number of lines tall. After producing the last line of a sprite on the screen, a sprite DMA channel may be used to produce yet another sprite image elsewhere on screen (with at least one horizontal line between each reuse of a sprite processor). Thus, many small sprites can be produced by simply reusing the sprite processors appropriately. * Dynamically controllable inter-object priority, with collision detection. This means that the system can dynamically control the video priority between the sprite objects and the bitplane backgrounds (playfields). You can control which object or objects appear over or under the background at any time. Additionally, you can use system hardware to detect collisions between objects and have your program react to such collisions. * Custom bit blitter used for high speed data movement, adaptable to bitplane animation. The blitter has been designed to efficiently retrieve data from up to three sources, combine the data in one of 256 different possible ways, and optionally store the combined data in a destination area. The bit blitter, in a special mode, draws patterned lines into rectangularly organized memory regions at a speed of about 1 million dots per second; and it can efficiently handle area fill. * Audio consisting of four digital channels with independently programmable volume and sampling rate. The audio channels retrieve their control and sample data via DMA. Once started, each channel can automatically play a specified waveform without further processor interaction. Two channels are directed into each of the two stereo audio outputs. The audio channels may be linked together to provide amplitude or frequency modulation or both forms of modulation simultaneously. * DMA controlled floppy disk read and write on a full track basis. This means that the built-in disk can read over 5600 bytes of data in a single disk revolution (11 sectors of 512 bytes each).
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