Amiga 2000 Technical Information

http://www.nationalamiga.com/a-2000.html (Amiga Plus Extra No. 5/97, 05/1997)

Amiga 2000 Series Technical Information


KICKSTARTS:
 1.2 in ROM
 1.3 in ROM
 2.04 in ROM
 3.1 in ROM
 Amiga Unix (with Commodore 2620 or 2630 Accelerator)

 ROM chip is a 40-pin DIP

CPU:
 68000 at 7.14MHz for Amiga 2000
 68020 at 14MHz for Amiga 2500/020 (Commodore 2620 in CPU slot)
 68030 at 25MHz for Amiga 2500/030 (Commodore 2630 in CPU slot)

FPU:
 None for base Amiga 2000
 68881 at 14MHz for Amiga 2500/020 (Commodore 2620 in CPU slot)
 68882 at 25MHz for Amiga 2500/030 (Commodore 2630 in CPU slot)

CHIPS:
 Denise - Originally shipped with 8362 Denise, REV6.3 and up motherboard
          had 8373 SuperDenise
 Paula  - Standard Paula
 Agnus  - DIP Agnus
 Gary   - Standard Gary
 Buster - ZorroII Buster DIP

RAM:
 All Amiga 2000 series machines have 1 megabyte of RAM soldered to
  the motherboard.
 The German 3.x series had 512k on the motherboard and 512k in CPU slot
 All 4.x motherboards had RAM set up as 512k CHIP and 512k FAST.
 All 6.x motherboard had RAM set up as 1 Megabyte CHIP.
 4.x motherboards can be converted easily to 1 Megabyte of CHIP RAM with
  a new Agnus and some cutting. Here's how.

PORTS:
 15KHz Video
 Parallel Port
 External Disk Drive
 Left and Right RCA Audio
 Serial Port
 Joystick Ports
 5-pin DIN Keyboard Port

SLOTS:
 1  Video Slot
 1  86-pin CPU Slot
 5  ZorroII 16-bit Expansion slots
 2  8-bit ISA slots (for use with BridgeBoard Devices)
 2  16-bit ISA slots in-line with 2 Zorro slots (for use with BridgeBoard Devices)

MOTHERBOARD REVISIONS:
 Pre 4.x were German motherboards. Not recommended for use at all.
 4.2
 4.3
 4.4
 4.5 Last in the 4.x series
 6.0 Has ROM tower for Kickstart, buggy with some expansion cards.
 6.2 Removed ROM tower for Kickstart that was on 6.0 board.
 6.3 Now has KS2.04 ROM, 8375 Agnus and 8373 SuperDenise as standard
 6.5 Have not seen one

MotherBoard Revisions according to Dave Haynie:

A2000-A german, like an A1000 in a different box, 512k CHIP, non-standard processor and video slots

Yes. The orginal A2000 was designed in Germany. It was based on an integration of the A1000 motherboard design and the example Zorro II backplane from "Schematics and Expansion Specifications", the A1000 hardware manual. It used the thin Agnus, which handled only 512K of DRAM. They added a "Genlock" slot, which was essentially just the 23-bit video signals on an internal connector, and the "MMU" slot, which was essentially just the A1000 external edge connector on an internal slot. The machine shipped with 512K of Fast RAM in this slot, though the case was slow and had some reliability problems. About 60,000 of these machines were made, so I've heard.

A2000-B Redesigning The German Model

This was the original A2000-CR (Cost Reduced) that I designed. I took the A500 chip set and integrated most of the control logic for the expansion bus into a gate array called Buster (the original thin Buster). This board was code-named the "B2000", not out of any special letter-sequencing, but because it was made from some A500 parts -- the A500's code-name was the "B-52".

To to the German design, I added a second video connector, which brought out the remaining 8-bits of digital the video signal and some parallel port lines (just in case someone needed a way to control something out there). I also designed a "coprocessor interface" for the internal CPU slot, which allowed processor cards to be added without the need to remove the 68000. And of course, given the much higher integration (thanks to Buster, Gary, Fat Agnus, etc), I was able to fit 1MB of RAM on the motherboard, even though I went to a 2-layer board (management's demands for cost, not my idea, though I did may it work OK.)

REV 3.9

About 200 pre-production B2000s were released, as "Dealer Demo" units, never meant to be sold. That's labelled Rev 3.9, of course some dealers sold them, since the A2000 was hot. These may have problems with CPU slot devices since, like the orginal A2000, there was no additional buffering on the clocks that drove that slot (and timing is very critical in many CPU slot applications).

REV 4.x Series

The Rev 4 A2000 was around most of the system's life. This was really just the Rev 3.9 with all the finalized changes. Extra buffering splits Agnus clocks between internal, expansion, and CPU slots. Rev 4.1 immediately corrected one missing signal on the secondary video slot (no pain Rev 4.0 boards were released). Rev 4.2 was some kind of production fix, I think it removed some overzealous FCC hacks, like the extra filter capacitors on the keyboard connector. Rev 4.3 tweaked a few pullup resistor values, to adjust for differences in the new CSG-made Gary chip (a full custom part) versus the Toshiba-made Gary chip (a gate array). After some 150,000 or so A500/A2000s, the CSG Gary was phased in. Rev 4.4 I believe made some changes to filtering of the TICK line, to account for some new power supplies that had been particularly noisy on that line. Rev 4.5 increases the value of the pullup resistor on the BAS* line of the expansion bus; there was a strange problem in conjunction with expansion bus DMA turnaround (what happens after a DMA device gives the bus back), BAS*, certain vendors of the 74ALS245 buffer that sits between BAS* and the local bus's AS*, and accelerator cards that could cause crashes. Add a 1K or so pullup to pins 11 and 20 of U605 on pre-4.5 boards to fix this problem (this was the only severe problem addressed by any subrevision).

REV 6.x Series

The Rev 6 A2000 was never called the A2000C, except maybe by geeks on usenet :-). The Rev 6 A2000 changed the DRAM array from 256K x 1 parts to 256K x 4 parts. Some layout and FCC changes were made, I don't know just what, I was kind of out of the picture at the time (Rev 5 was just Rev 4.5 with the DRAM changes, nothing else. Rev 6 did more, I wasn't really involved). The original Rev 6 board has some noise problems on the expansion bus, possibly due to a new production of 68000s from Motorola that happed to be used at the same time. Rev 6 also had some extra noise on its time-of-day clock. Rev 6.1 corrects the clock noise, Rev 6.2 addresses the expansion bus noise.

Thanks to Phil Kernick for sending the Dave Haynie message to National Amiga.

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