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© 1997-2006
Gareth Knight
All Rights reserved



Amiga Custom Chipset

The power behind the Amigas technology lies in its interdependency of hardware- different functions are controlled by different chips, allowing the processor to perform other tasks.

The Copper
The Copper is a co-processor integrated into Agnus. It uses Chip RAM to control the graphic system, considerably easing the strain on the 68k processor. The co-processor can also intervene directly on controls of the other components. It is responsible for the management of the Blitter. One of the Amigas limitations is the Copper's use of just Chip RAM, restricting the display to just 2Mb. However, for its limitations it has contributed to creating part of the Amiga 'look and feel' providing the capability to drag a screen and show several screens at once.

The Blitter
Like the Copper the Blitter is a co-processor integrated into Agnus. Its function is to display memory zones as efficiently as possible- the Blitter performs this function twice as fast as the 68000. With the Blitter you can copy rectangular image parts extremely fast to other areas. During this, you can take up to three source data areas and perform operations on them. Like the Copper, the Blitter is restricted to Chip RAM access limiting its use. Operations undertaken by the Blitter are called Blits. The Blitter works in an asynchrone manner, allowing the 68k to continue to function normally during blits.On higher specification Amigas the Blitter has been superceded by software C2P (Chunky to Planar) functions or retargetable graphics. A good comparison of Blitter vs. Fast RAM implementation can be seen in Xtreme Racing.

Agnus (Address GeNerator Unites) is probably the most known of the Amiga custom chips. It exists in different forms, ranging from the original found in the A1000 to the "Super" found in the A3000. Apart from minor changes the main difference between these versions is the amount of memory to which they have access. Agnus is responsible for DMA access, clock frequency generation in the A500 and A2000, and allows access to Chip RAM by the custom chips. This has ranged from 512k to 2Mb, that have upgraded from Agnus to Super Fat Agnus. The A500 and A2000 can increase the amount of Chip RAM available through the addition of a third party 2Mb upgrade.

Short for Display Encoder, Denise is responsible for the generation of colours and display different resolutions. It controls hardware sprites used by the system. The Super version of  the Denise present in the ECS chipset and called Fat Denise in the A3000. The upgrade added a number of new modes to the Amiga display, allowing the use of standardised resolutions, ranging from 640x480 in 2 bitplanes (Productivity mode) to 1280x515 in 2 bitplanes (called SuperHires). It was called Daphne in the A1000 and in early advertisements of the A500.

Paula (Port Audio Uart and Logic) controls generation of the 8-bit audio and contains control circuits for floppy access, mouse, keyboard, and some external ports. It was called Portia in the A1000.

Alice was the successor to the Agnus in the AGA upgrade. It includes the same 16-bit data bus interface, Alice is nevertheless capable of 23-bit access.

Lisa is a member of the AGA chipset, replacing the ECS Denise.

Gary controls access to the bus, as well as the diskette reader. The Gary custom chip has been upgraded over time- the A3000 implemented Fat Gary and, among others functions the A4000 implementation manages the IDE port.

Found on the A600 and A1200, Gayle replaces Gary adding supplementary functions to the outdated chip. It manages Chip RAM, 8520, IDE bus and the connection of memory card.

Found in the A3000 and A4000, Ramsey manages Fast RAM and generates addresses during DMA transfer.

The CIA's (Complex Interface Adaptor) manage parallel and serial port I/O, clock, joystock, etc, as well as some system interrupts.

Found on the A3000, Amber manages the deinterlacer by synchronizing and controlling the necessary signals for video memory to the display. It is also found on the Commodore A2320 flicker fixer card. Amber is named after the designer's daughter.

Solely present in the CD32, this chip upgrades the Amiga custom chipset to use Chunky pixels through a Chunky 2 Planar conversion process, used for 3D games such as Doom. It also manages CD-ROM data and replaces some of the functions of Gary and Gayle.


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