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. According to Jay Miner, original Agnus was fabricated in 5 μm manufacturing process like all OCS chipset. The Blitter and Copper are also contained here.

Agnus features:
 * The Blitter, a bitmap manipulator. The Blitter is capable of copying blocks of display data, or any arbitrary data in the on-board 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
 * Memory controller (memory that can be accessed by the processor and the chipset)
 * 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



 * OCS Agnus which can address up to 512 kB of Chip RAM (PLCC versions add 512 kB of pseudo-fast RAM)
 * 8361 (DIP) - Amiga 1000 (NTSC); Amiga 2000 model A (NTSC)
 * 8367 (DIP) - Amiga 1000 (PAL); Amiga 2000 model A (PAL)
 * 8370 (PLCC) - Amiga 500 to Rev 5.x (NTSC); Amiga 2000 model B to Rev 4.5 (NTSC)
 * 8371 (PLCC) - Amiga 500 to Rev 5.x (PAL); Amiga 2000 model B to Rev 4.5 (PAL)
 * ECS Agnus which can address up to 1 MB of Chip RAM
 * 8372 - no data *
 * 8372A - Amiga 500 from Rev 6 (NTSC/PAL); Amiga 2000 model B from Rev 6.0 to Rev 6.3 (NTSC/PAL); Commodore CDTV
 * 8375 (318069-16 only) (PAL) - Amiga 500 from Rev 6 (PAL); Amiga 2000 model B from Rev 6.4 (PAL)
 * 8375 (318069-17 only) (NTSC) - Amiga 500 from Rev 6 (NTSC); Amiga 2000 model B from Rev 6.4 (NTSC)
 * ECS Agnus which can address up to 2 MB of Chip RAM
 * 8372AB - Amiga 3000 from Rev 6.1 to Rev 8.9 (NTSC/PAL)
 * 8372B - Amiga 3000 Rev 9 (NTSC/PAL)
 * 8375 (PAL) - Amiga 500 Plus; Amiga 600 (PAL)
 * 8375 (NTSC) - Amiga 600 (NTSC)

* 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 Fat Agnus 1MB and Fat Agnus 2MB usually known as Super Agnus; Super Fat Agnus; Fatter Agnus; Big Agnus; Big Fat Agnus, but these aren't official names.

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