The Agnus is responsible for controlling around 25 system DMA channels, the generation of various system clocks in some Amiga's, and for addressing Chip RAM. Infact, Chip Memory is so called because it's addressable by the system's custom chips, unlike Fast Memory. The Agnus also contains an integrated Copper (co-processor) which controls aspects of the Amiga's display such as draggable screens, and the infamous "copper scrolls". The Amiga's blitter is also located in the Agnus chip and is responsible for moving rectangular areas of memory efficiently as possible. This may not sound particularly spectacular, but the blitter is twice as fast as the 68000 at moving blocks of memory and is capable of doing it asynchronously from the 68000, meaning the processor is totally free for other operations. The blitter is particularly useful for graphics operations. Agnus is part of the OCS & ECS chipset found in the 68000-based A500/A600/A1000/A2000/CDTV systems, and the A3000D/T models. It's equivalent in the AGA-based machines is Alice.
| Chip Name |
Chip Number |
Part Number |
Used In |
| Agnus (512K) |
8361 |
252125-01 |
A1000 (NTSC), A2000A (NTSC), DIP |
| Agnus (512K) |
8361 R3 |
|
A1000 (NTSC), A2000A (NTSC), DIP |
| Agnus (512K) |
8367 |
252362-01 |
A1000 (PAL), A2000A (PAL), DIP |
| Agnus (512K) |
8370 |
318070-01 |
A500/A2000 (NTSC) |
| Agnus (512K) |
8371 |
318071-01 |
A500/A2000 (PAL) |
| Agnus (1MB) |
8372 |
318069-02 |
A500/A2000 (PAL/NTSC) Regular Type |
| Agnus (1MB) |
8372A |
318069-029 |
A500/A2000 (PAL/NTSC) (changed after some damage) |
| Agnus (2MB) |
8372AB |
318069-03 |
A3000D/T (PAL/NTSC) |
| Agnus (2MB) |
8372B |
318069-03 |
A3000D/T (PAL/NTSC), early MegAChip (PAL/NTSC) |
| Agnus (2MB) |
8375 |
390544-01 (1) |
A500+/A600 (PAL) - same as 318069-10 |
| Agnus (2MB) |
8375 |
390544-02 (1) |
A500+/A600 (NTSC) - same as 318069-11 |
| Agnus (2MB) |
8375 R2 |
318069-10 (1) |
A500+/A600 (PAL), later MegAChip (PAL) |
| Agnus (2MB) |
8375 R2 |
318069-11 (1) |
A500+/A600 (NTSC), later MegAChip (NTSC) |
| Agnus (1MB) |
8375 / 8375 R1 |
318069-16 |
A500+/A600 (PAL) - Spare part 8372A pin-out (2) |
| Agnus (1MB) |
8375 / 8375 R1 |
318069-17 |
A500+/A600 (NTSC) - Spare part 8372A pin-out (2) |
| Agnus (2MB) |
8375 / 8385 R0 |
318069-18 |
A3000D/T (PAL) - Spare part 8372B pin-out (2) |
| Agnus (2MB) |
8375 / 8385 R0 |
318069-19 |
A3000D/T (NTSC) - Spare part 8372B pin-out (2) |
(1) The part number shift from 318069-xx to 390544-xx, then back to 318069-xx, was an internal C= administrative blunder. The 390544-01/02 pair of chips are the same as the 318069-10/11 chips.
(2) The later 8375 parts (318069 -16/17 and -18/19) are C= spare parts for the earlier pin-out 8372A 1MB and 8372B 2MB Agnus used in the A500/2000 & A3000 respectively. They have VBB markings, and will require a field mod on the motherboard in most cases, as one signal pin's use has changed. It is related to the NTSC/PAL signal (detected at boot-up) which originally came from the motherboard/hardware, but was instead built into the later chip fabriation.
The presence of R0/R1/R2/R3/etc markings next to the 837#x general part identifiers have not shown to have any identifiable differences in behvior in the field. Speculation is that it may have been something CSG added for production-process identifications, but this is not confirmed. Use the XXXXXX-XX part numbers to properly identify the model, particularly with the PLCC-84 pin package.
The 8375-series chips with 318069-xx part numbers values from 12-15 were to have been used in products which were never made/released. The internal C= information on them was later found, mentioning their definitions. They were again PAL/NTSC pairs, and of 1MB or 2MB memory-addressing, but may have had unique pin-outs vs other produced chips. They were not included here because of the high amount of confusion that already exists with the common Agnus parts.