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Custom Chips

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 first a copy of Wikipedia with beginning changes to this amigawiki

In addition to the Amiga chipsets, various specially designed chips have been used in Commodore Amiga computers that do not belong to the 'Amiga chipset' in a tight sense.


Gary, short for Gate Array, has been used in the Amiga 500, 2000(B) and CDTV. Gary provides glue logic for bus control and houses supporting functions for the floppy disk drive. It integrates many functions built discretely in the previous Amiga 1000 in order to reduce costs.

Fat Gary

Fat Gary was Gary's upgrade for the 32-bit A3000/T and A4000/T.


Gayle replaced Gary in the A600 and A1200. It also incorporates the control logic for the PCMCIA and internal ATA interface on these systems.


Buster is the expansion BUS conTrollER<ref>Name according to Dave Haynie's eBay listing of the Fat Buster “tower” prototype in April 2011</ref> and was used in the Amiga 2000(B), integrating discrete logic from the original A2000(A). Buster controls bus arbitration and DMA for the Zorro II expansion subsystem.

Super Buster (Fat Buster)

The Amiga 3000 and 4000 lines use Super Buster<ref>[ The Dave Haynie Archives - Fat Buster II specifications]</ref> for bus control and arbitration of both Zorro II and Zorro III subsystems. Super Buster's development was never really finished,<ref>[ Big Book of Amiga Hardware/Custom Chips/Buster]</ref> so there are various levels of compatibility:

  • Level I - up to rev 7 (A3000), only provides support for basic Zorro III without DMA.
  • Level II
    • rev 9 (A4000) is slightly faster than Level I. It provides DMA support, but has a bug that might lead to a bus lockup.
    • rev 11 (A4000T and aftermarket) provides DMA support for a single bus master. 16 MHz A3000 requires a 25 MHz upgrade for Buster11 to work.

All revisions fully support Zorro II PIO and DMA.


All Amiga computers use two 8520 CIAs (Complex Interface Adapter) for peripheral interfacing and the system timers. These chips were also used in some other Commodore devices.

  • 'Even' CIA functions: floppy control, serial control, some parallel port status
  • 'Odd' CIA functions: parallel port, keyboard, some floppy support, joystick/mouse buttons.

Ramsey & (Super) DMAC

In the A3000 and A4000 series, Ramsey controls the on-board 32-bit Fast RAM and provides address generation for SDMAC. The SDMAC in the A3000/T provides DMA and bus interface for the integrated WD33C93A SCSI controller.

Officially, SDMAC rev 02 requires a Ramsey 04, and SDMAC 04 a Ramsey 07 counterpart.<ref>[ Big Book of Amiga Hardware: Ramsey]</ref> but SDMAC 04 + Ramsey 04 and even SDMAC 02 + Ramsey 07 combinations have been reported to work as well.<ref>[ thread on A3000 chip revisions]</ref>

The previous 16-bit DMAC used in A2091/A590 SCSI adapters also includes 24-bit address generation.


Amber was used in the A3000(T) and on the A2320 Flicker Fixer expansion for the A2000. Amber buffers alternate video fields in three 256Kx4 field memory chips to convert interlaced output to progressive format. Amber can accurately sample Lo-res and Hi-res modes but drops every other pixel in SuperHi-res (35 ns pixels) mode. Non 15 kHz modes are automatically bypassed to the monitor without buffering or changing frequencies. Amber was also designed to work without expensive field memory as a simple scan doubler, but has not been marketed that way.


Used in the A1200, Budgie connects the trapdoor expansion port for Zorro II-like expansions and controls additional Fast RAM.


Bridgette is an integrated bus buffer in the A4000 series. It connects the chip, CPU and I/O buses.


'Akiko' is the CD32's all-purpose 'glue' chip and forms part of the AGA chipset used in that system. Akiko is responsible for implementing system glue logic, some of the control logic for the CD32's CD-ROM controller, and controlling the serial ('AUX') port.<ref>title=The Big Book of Amiga Hardware - Custom Chips: Akiko|url=</ref>

Additionally, the Akiko chip is able to perform simple 'chunky' to 'planar' graphics conversion in hardware. The Amiga's native display is a planar display which is simple and efficient to manipulate for routines like scrolling. However, chunky displays are faster and more efficient for 3D graphics manipulation. Akiko allows this conversion to be performed in hardware instead of relying on software conversion which would cause more overhead. The conversion works by writing 32 chunky pixels to Akiko's registers and reading back eight 32-bit words of converted planar data which can then be copied to the display buffer.


The Vidiot is a videot that works as for the OCS/ECS generation's 12 bit video to analogue RGB output. It also generates a monochrome composite video signal and combined sync. The A3000 uses one Vidiot each for 15 kHz video and for 31 kHz (Amber) output. AGA Amigas use off-the-shelf DACs.


The Kickstart ROM is not a custom chip but a mask-programmed ROM chip for most versions. It contains the largest part of the operating system. Kickstart 1.x ROMs have a capacity of 256 kiB, Kickstart 2.x and 3.x contain 512 kiB. 32-bit Amigas use a pair of 16-bit chips to provide full width access. Later not mass produced upgrade versions were often realized with PROMs or EPROMs.

See also


  • Commodore Amiga 500/2000 technical reference manual
  • A3000 system schematics, March 1990
  • A4000 system schematics, March 1992

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Last modified: 2013/02/24 07:16