my-server
← Wiki

MOS Technology Agnus

The MOS Technology "Agnus", usually called Agnus, is an integrated circuit in the custom chipset of the Amiga computer. The Agnus, Denise and Paula chips collectively formed the OCS and ECS chipsets.

The Agnus is the Address Generator Chip. Its main function, in chip area, is the RAM Address Generator and Register Address Encoder which handles all DMA addresses. The 8361 Agnus is made up of approximately 21000 transistors and contains DMA Channel Controllers. The Blitter and Copper are also contained here. Originally Agnus was fabricated in 5 ÃŽÂ¼m manufacturing process like all OCS chipset.

Agnus features:

  • Memory controller ("Chip" memory that can be accessed by the processor and the chipset)
  • The Blitter, a bitmap manipulator. The Blitter is capable of copying blocks of display data, or any arbitrary data in the chip memory, at high speed with various raster operations as well as drawing pixel perfect lines and filling outlined polygons, while freeing the CPU for concurrent tasks.
  • "Copper", a display synchronized co-processor
  • 25 Direct Memory Access (DMA) channels, allowing graphics, sound and I/O to be used with minimal CPU intervention
  • DRAM refresh controller
  • Generates the system clock from the 28 MHz oscillator
  • Video timing

Agnus was replaced by Alice in the Amiga 4000 and Amiga 1200 when the AGA chipset was introduced in 1992.

Chips by capability

<nowiki>*</nowiki> Somewhere 8372A Agnus mentioned as simply "8372".

Chips by package

  • 48-lead DIP Agnus (aka thin Agnus): 8361; 8367
  • 84-contact PLCC Fat Agnus (named Fat Lady on most Amiga 2000 motherboards) 8370; 8371; 8372; 8372A; 8372AB; 8372B; 8375

Notes<br>Fat Agnus 1MB and Fat Agnus 2MB also known as Super Agnus; Super Fat Agnus; Fatter Agnus; Big Agnus; Big Fat Agnus.

DMA Channels

Pinout

PLCC versions

When replacing or upgrading chips, pinouts need to be taken care of. Types are just mentioned for reference; four-digit types and pinouts/usage are not consistent.

References: A500 Service Training, A3000 Service Manual, A500+ Service Manual, A1200 schematics

See also

References

Sources
Notes