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 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.
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the Blitter has been superceded by software C2P (Chunky to Planar)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
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
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.