Commodore Amiga Retro

Data Sheet

Model Range:

A1500
A2000
A2000HD
A2500/020
A2500/030
A2500UX

Released in 1987 as Commodore's first high end expandable
machine. Though early models were based around the A1000
design, the later models were built around the A500 chipset.

The hard drive version named the A2000HDcame with an A209x
SCSI controller and a SCSI hard disk drive. The A2500 version
has a processor card added to the A2000HD configuration. The
A1500 was aimed primarily at the UK market and was fitted with
two floppy drives but no hard disk drive. The A2500UX came with
AT&T Unix System V Release 4 operating system instead of AmigaOS,
and had a three button mouse, and often with a tape streamer
and Ethernet card.

Processor
68000 @ 7-28 MHz
68020 @ 7-25 MHz
68030 @ 16-50 MHz
68040 @ 25-40 MHz
68060 @ 50 MHz

The A1500 and A2000 have a socketed 68000 @ 7.14 MHz 
processor on the motherboard and were fitted with an empty 
processor slot.

The A2500 uses a processor card. The A2500/020 came with 
an A2620 processor card featuring a 68020 and 68881 @ 14 MHz, 
and the A2500/030 came with an A2630 featuring a 68030 and 
68882 @ 25 MHz.

Memory
up to 2 MB Chip RAM
up to 128 MB Fast RAM on processor cards
up to 8 MB Fast RAM on Zorro II expansion cards

the majority of A2000's have 1 MB RAM soldered to their 
motherboard. Early models, the 3.x series, have 512 kB 
Chip RAM on their motherboard and 512 kB Fast RAM on the 
processor card. The 4.x series have both 512 kB Chip and 
Fast RAM soldered to the motherboard, whilst the 6.x series 
have the RAM set up as 1 MB Chip RAM. Chip RAM can be expanded 
to 2 MB with third party expansions which replace the Agnus 
chip. 24 bit Fast RAM can be added using Zorro II expansion 
cards up to 8 MB, and 32 bit Fast RAM using processor cards 
featuring a 68020 or better.

Custom chips
Agnus / Fat Agnus - OCS / ECS display controller
Denise / Super Denise - OCS / ECS display encoder
Paula - audio and I/O controller
Gary - system address decoder
Buster - DMA arbitrary controller

The A2000 OCS or ECS chip set offers the same screen modes as
the A500 and A500 Plus:

 A500  A500+
Low High Low High Super
PAL, non-interlaced
PAL, interlaced
NTSC, non-interlaced
NTSC, interlaced 320×256
320×512
320×200
320×400 640×256
640×512
640×200
640×400 320×256
320×512
320×200
320×400 640×256
640×512
640×200
640×400 1280×256
1280×512
1280×200
1280×400 50 Hz, 15.60 kHz
50 Hz, 15.60 kHz
60 Hz, 15.72 kHz
60 Hz, 15.72 kHz
Euro36
A2024  320×200 - 1280×400
1024×1024 73 Hz, 15.76 kHz
15 Hz, 15.72 kHz
Multiscan
Euro72
Super72  640×480 - 640×960
640×400 - 640×800
400×300 - 800×600 60 Hz, 31.44 kHz
70 Hz, 31.43 kHz
72 Hz, 24.62 kHz

Using the OCS chip set the A2000 supports either PAL or 
NTSC screen modes, though not both. Low resolution screen 
modes offer up to 32 colours from a palette of 4096, 64 in 
EHB mode or 4096 in HAM mode. High resolution screen modes 
give 16 colours from 4096, super-high resolution and 
productivity modes offer 4 colours from a palette of 64. 
Other screen modes require a Zorro graphics card.

The A2000 series has 4 channel stereo 8 bit audio output
with frequencies up to 28 kHz using screen modes with 15 kHz,
or up to 56 kHz when using screen modes with higher horizontal
frequency. 16 bit audio is supported when used on Zorro
sound card. A2000s with the OCS chip set shipped with 
Kickstart 1.2 first, later with 1.3. The ECS models all 
shipped with 2.04 Kickstart ROM. All versions can be replaced 
with a 3.1 one.

Expansion slots
1× processor card slot (CPU slot)
5× Zorro II slots
1× video slot
2× inactive AT ISA slots
2× inactive XT ISA slots

Zorro, ISA and video slots are all fitted to the motherboard.
Two AT ISA slots in line with a Zorro II slot, while the XT and
video slots are not.

The four ISA slots have their power and ground pins activated 
only. To access the slots with the A2000 a BridgeBoard has to 
be fitted. With a BridgeBoard installed, two or three ISA 
compatible cards can be used depending on the BridgeBoard's 
position - if a bridgeboard is not installed in slot 3 two ISA 
and four Zorro cards can be used, if it is in slot 4 three 
ISA and three Zorro cards are possible. Inactive ISA slots 
can be used for non intelligent cards like TBCs or fan cards. 
The two XT ISA slots can be upgraded to AT slots by simply 
soldering the 16 bit extension slots.

Early versions of the A2000 have an internal version of the 
A1000 external edge connector as a processor card slot. All 
other versions use an 86 pin processor card slot with a 
coprocessor interface. This allows processor cards to be 
added without the need to remove the 68000.

The A2000 was a very versatile computer with many upgrade options.

Drive bays
2× 3.5" front bays
1× 5.25" front bay

In the A2000 one, in the A1500 both of the 3.5" bays are 
occupied with 880 kB double density floppy disk drives.

Interfaces
1× serial DB25 male, RS232
1× internal serial 26 pin header
1× parallel DB25 female, Centronics
1× video DB23 male, analog RGB
1× composite, black & white
2× mouse/game DB9 male
2× stereo audio RCA jack
1× keyboard 5 pin DIN female
1× external floppy DB23 female
1× internal floppy 34 pin header

The floppy drive controller supports up to four devices. 
That is two attached to the internal floppy header and two 
connected to the external floppy port. Both double and high 
density disk drives are supported. The internal serial header 
has the same address as the external one. It is intended to 
be used with internal MIDI interfaces.

Motherboard revisions
A2000-A: ()
An integration of the A1000 motherboard design and an example 
Zorro II  backplane. It uses the thin Agnus (DIP) which handles 
only 512 kB RAM. The video slot is just an internal version 
of the external video port with the processor card slot as an 
internal version of the A1000 external edge connector. The 
A2000-A was a touch unreliable. The Buster chip is missing, 
as is the composite output connector. Memory is configured
as 512 kB Chip RAM on the motherboard and 512 kB Fast RAM 
in the processor slot.

A2000-B:
This is a cost reduced version based around the A500 chip set. 
Most of the control logic for the expansion bus is integrated 
into the Buster chip. The video slot is extended with more 
signals and the CPU slot has a coprocessor interface. A black 
and white composite video connector is provided. 1 MB of RAM 
is placed on the motherboard.

revision 3.9
This was a pre-production A2000-B intended for demonstration 
purposes which may have problems with processor cards given 
that there is no additional buffering on the clocks that drive 
the CPU slot

revision 4.0
Offering extra buffering splits Agnus clocks between the 
expansion and CPU slots

rev 4.1
Utilising correction of one missing signal on the video slot
No rev 4.0 boards were released because of this bug

rev 4.2
Evidently a number of unnecessary filter capacitors were 
removed to fix the character loss for HITEK type keyboards

rev 4.3
A Toshiba manufatured Gary chip is replaced with a CSG (MOS) one,
pull-up resistors added to support it

rev 4.4
Changes implemented to filtering of a noisy line, cost reduction

rev 4.5 ()
Problems fixed in conjunction with expansion bus DMA turnaround
uses Kickstart 1.3

revision 5.0
Motherboard RAM configured to use 256k×4 chips instead of 
256k×1 ones

revision 6.0
Minor layout and FCC changes

rev 6.1
A reset IC added to clean up RAM retention and correction of 
the noise on the "time of day" clock Uses Agnus 8372

rev 6.2 ()
Added correction to the noise on the expansion bus caused 
by a new production of 68000s

Fixes  to get certain expansion boards to work correctly with 
256k×4 DRAMs and Agnus 8372

rev 6.5
Upgrades to use Kickstart 2.04 ROMs and the ECS chip set: 
Fat Agnus, Super Denise

Power supply revised to 220 W power output
2× standard 4 pin power connectors
2× mini 4 pin floppy drive power connectors.

There really has never been such a heavily modified and upgraded
model of computer. The A2000 was a magic piece of kit.