MOS Technology Agnus explained

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.

DMA Channels

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

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.^[1]

Pin	OCS/ECS	ECS		AGA (Alice)	Description
	A500/2000	A3000	A500+/600	A4000/1200
	8370/1	8372	8375	8374
1	RD13	DRD13	DRD13	DRD13	Data Bus 16 bit, bit 13
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	Data Bus 16 bit, bit 0
15	Vcc	Vcc	Vcc	Vcc1	+5V ±5%
16	RST*	_RESET	_RESET	/RESET	Global RESETn, low active
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	Memory address bus 9 bit, bit 0 (except 8375 which is bit 1)
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	Memory address bus 9 bit, bit 8 (except 8375 which is bit _LDS)
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	Ground, common on whole board
83	RD15	DRD15	DRD15	DRD15	Data Bus 16 bit, bit 15
84	RD14	DRD14	DRD14	DRD14	Data Bus 16 bit, bit 14

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

References

Sources

AMIGA 1000 ASSEMBLY LEVEL REPAIR (Commodore-Amiga, Inc.) 1985 PN 314038-01 Dave's Amiga Schematics and Manuals
Commodore Amiga A500/A2000 Technical Reference Manual (Commodore-Amiga, Inc.) 1987 Dave's Amiga Schematics and Manuals
A500 SYSTEM SCHEMATICS COMPONENT PART LIST (Rev 6A/7) Dave's Amiga Schematics and Manuals
A3000 SYSTEM SCHEMATICS (Commodore Business Machines, Inc.) March, 1990 PN-314677-01 www.1000bit.net
CDTV SERVICE MANUAL (Commodore International Spare GmbH) May, 1991 PN-400403-01 www.ianstedman.co.uk (ZIP-file)
A500 PLUS SERVICE MANUAL (Commodore International Spare GmbH) October, 1991 PN-400420-01 www.1000bit.net
A600 SYSTEM SCHEMATICS (Commodore International Spare GmbH) April, 1992 PN-400422-02 www.1000bit.net
OBLIGEMENT: les chipsets de l'Amiga
Big Book of Amiga Hardware
alexh on English Amiga Board (Agnus 8372B info)
National Amiga Inc. mirrored on l8r.net
Marketed Commodore Amiga models
AMIGA Auckland Inc.
Amiga University
Commodore Computer Online Museum

Notes

Notes and References

Difference of 8372A vs 8375 . George Robbins . 14 October 1992 . comp.sys.amiga.hardware . 35861@cbmvax.commodore.com . 1 October 2018 .