MOS Technology Agnus

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The MOS Technology "Agnus", usually called Agnus is an integrated circuit in the custom chipset of the Commodore 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 image 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[edit]

* Somewhere 8372A Agnus mentioned as simply "8372".

Chips by package[edit]

  • 48-lead DIP Agnus (aka thin Agnus): 8361; 8367
  • 84-contact PLCC Fat Agnus (named Fat Lady on most Amiga2000 mainboard) 8370; 8371; 3872; 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; Super Fat Agnus, but these aren't official names.

DMA Channels[edit]

Priority Name Count Cycles/Rasterline Chip Notes
MPU 1 varying CPU
A Blitter 4 varying Agnus (internal) yields 1/4 cycles to CPU when BLTPRI not active
B Bitplane 6 80 Denise impairs sprite channels on severe overscan
C Copper 1 varying Agnus (internal)
D Audio 4 4 Paula
E Sprites 8 16 Denise
F Disk 1 3 Paula
G Memory Refresh 1 4 -
Reference: Amiga 500 plus Service Manual

Pinout[edit]

PLCC Versions[edit]

When swapping/upgrading chips pinouts need to be taken care of. Types are just mentioned for reference, four-digit types and pinouts/usage are not consistent.[1]

  OCS/ECS ECS ECS AGA (Alice)
  A500/2000 A3000 A500+/600 A4000/1200
  8370/1 8372 8375 8374
1 RD13 DRD13 DRD13 DRD13
2 RD12 DRD12 DRD12 DRD12
3 RD11 DRD11 DRD11 DRD11
4 RD10 DRD10 DRD10 DRD10
5 RD9 DRD9 DRD9 DRD9
6 RD8 DRD8 DRD8 DRD8
7 RD7 DRD7 DRD7 DRD7
8 RD6 DRD6 DRD6 DRD6
9 RD5 DRD5 DRD5 DRD5
10 RD4 DRD4 DRD4 DRD4
11 RD3 DRD3 DRD3 DRD3
12 RD2 DRD2 DRD2 DRD2
13 RD1 DRD1 DRD1 DRD1
14 RD0 DRD0 DRD0 DRD0
15 Vcc Vcc Vcc Vcc1
16 RST* _RESET _RESET /RESET
17 INT3 _INTR _INTR /INTR
18 DMAL DMAL DMAL DMAL
19 BLS* _BLISS _BLISS /BLS
20 DBR* _BLIT _BLIT /DBR
21 RRW _WE _WE /WE
22 PRW R/W R/W R/W
23 RGEN* _REGEN _REGEN _REGEN
24 AS* _AS _AS NC2
25 RAMEN* _RAMEN _RAMEN /RAMEN
26 RGA8 RGA8 RGA8 RGA8
27 RGA7 RGA7 RGA7 RGA7
28 RGA6 RGA6 RGA6 RGA6
29 RGA5 RGA5 RGA5 RGA5
30 RGA4 RGA4 RGA4 RGA4
31 RGA3 RGA3 RGA3 RGA3
32 RGA2 RGA2 RGA2 RGA2
33 RGA1 RGA1 RGA1 RGA1
34 28 MHz 28 MHz 28 MHz SCLK
35 XCLK A20 A20 A20
36 XCLKEN* _XCLKEN _CDAC 14 MHz
37 CDAC* _CDAC 7 MHz /CDAC
38 7 MHz 7 MHz CCKQ 7 MHz
39 CCKQ CCKQ CCK CCKQ
40 CCK CCK 14M CCK
41 TEST TEST GND /NTSC
42 Vss Vss1 DRA0 GND2
43 MA0 DRA0 DRA1 DRA0
44 MA1 DRA1 DRA2 DRA1
45 MA2 DRA2 DRA3 DRA2
46 MA3 DRA3 DRA4 DRA3
47 MA4 DRA4 DRA5 DRA4
48 MA5 DRA5 DRA6 DRA5
49 MA6 DRA6 DRA7 DRA6
50 MA7 DRA7 DRA8 DRA7
51 MA8 DRA8 _LDS DRA8
52 LDS* _LDS _UDS Vcc2
53 UDS* _UDS _CASL NC1
54 CASL* _CASL _CASU /CAS
55 CASU* _CASU DRA9 Vbb
56 RAS1* DRA9 _RAS1 DRA9
57 RAS0* _RAS _RAS0 /RAS
58 Vss Vss2 GND GND3
59 A19 A19 A19 A19
60 A1 A1 A1 A1
61 A2 A2 A2 A2
62 A3 A3 A3 A3
63 A4 A4 A4 A4
64 A5 A5 A5 A5
65 A6 A6 A6 A6
66 A7 A7 A7 A7
67 A8 A8 A8 A8
68 A9 A9 A9 A9
69 A10 A10 A10 A10
70 A11 A11 A11 A11
71 A12 A12 A12 A12
72 A13 A13 A13 A13
73 A14 A14 A14 A14
74 A15 A15 A15 A15
75 A16 A16 A16 A16
76 A17 A17 A17 A17
77 A18 A18 A18 A18
78 LP* _LPEN _LPEN /LPEN
79 VSY* _VSYNC _VSYNC /VSYNC
80 CSY* _CSYNC _CSYNC /CSYNC
81 HSY* _HSYNC _HSYNC /HSYNC
82 Vss Vss3 GND GND1
83 RD15 DRD15 DRD15 DRD15
84 RD14 DRD14 DRD14 DRD14

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

References[edit]