Amiga 500

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Amiga 500
Amiga500 system.jpg
A500 with 1084S monitor and second floppy drive
TypeHome computer
Release dateApril 1987 (Netherlands)
May 1987 (Europe)
October 1987 (US/UK)
Introductory priceUS$699, £499 (1987)
US$1,600 (2021 equivalent)
Discontinued1991 (1991)
Media880 KiB floppy disks
Operating systemAmigaOS v1.2 – 1.3 (upgradable up to 3.1.4 if 2 MB of RAM is installed)
CPUMotorola 68000 @ 7.16 MHz (NTSC) 7.09 MHz (PAL)
Memory512 or 1024 KiB 150 ns (maximum 9 to 138 MiB, depending on upgrades)[1]
Graphics736×567i 4 bpp (PAL)
736×483i 4 bpp (NTSC)
368×567i 6 bpp (PAL)
368×483i 6 bpp (NTSC)
Sound4× 8-bit channels PCM at max. 28 kHz with 6-bit volume in stereo
PredecessorAmiga 1000
SuccessorAmiga 500 Plus

The Amiga 500, also known as the A500, is the first low-end version of the Amiga home computer. It contains the same Motorola 68000 as the Amiga 1000, as well as the same graphics and sound coprocessors, but is in a smaller case similar to that of the Commodore 128,

Commodore announced the Amiga 500 at the January 1987 winter Consumer Electronics Show – at the same time as the high-end Amiga 2000. It was initially available in the Netherlands in April 1987, then the rest of Europe in May.[2] In North America and the UK it was released in October 1987 with a US$699/£499 list price. It competed directly against models in the Atari ST line.

The Amiga 500 was sold in the same retail outlets as the Commodore 64, as opposed to the computer store-only Amiga 1000. It proved to be Commodore's best-selling model, particularly in Europe.[3] Although popular with hobbyists, arguably its most widespread use was as a gaming machine, where its graphics and sound were of significant benefit.

Releases[edit]

In October 1989, the Amiga 500 dropped its price from £499 to £399 and was bundled with the Batman Pack in the United Kingdom (from October 1989 to September 1990) which included the games Batman, F/A-18 Interceptor, The New Zealand Story and the bitmap graphics editor Deluxe Paint 2.[4] Also included was the Amiga video connector which allows the A500 to be used with a conventional CRT television.

In late 1991, the enhanced Amiga 500 Plus replaced the 500 in some markets. It was bundled with the Cartoon Classics pack in the United Kingdom at £399, although many stores still advertised it as an 'A500'.[5]

The Amiga 500 series was discontinued in June 1992[6] and replaced by the similar Amiga 600. In late 1992, Commodore released the Amiga 1200, a machine closer in concept to the original Amiga 500, but with significant technical improvements. Despite this, neither the A1200 nor the A600 replicated the commercial success of its predecessor. By this time, the home market was strongly shifting to IBM PC compatibles with VGA graphics and the "low-cost" Macintosh Classic, LC, and IIsi models.[7]

Description[edit]

Outwardly resembling the Commodore 128[8] and codenamed "Rock Lobster" during development, the Amiga 500 houses the keyboard and CPU in one shell, unlike the Amiga 1000. It uses a Motorola 68000 microprocessor running at 7.15909 MHz (NTSC) or 7.09379 MHz (PAL). The CPU implements a 32-bit model, has 32-bit registers and 32-bit internal data bus, but it has a 16-bit main ALU, uses a 16-bit external data bus and 24-bit address bus, providing a maximum of 16 MB of address space.

The earliest Amiga 500 models use nearly the same Original Amiga chipset as the Amiga 1000.[9] So graphics can be displayed in multiple resolutions and color depths, even on the same screen. Resolutions vary from 320×200 (up to 32 colors) to 640×400 (up to 16 colors) for NTSC (704×484 overscan) and 320×256 to 640×512 for PAL (704×576 overscan.)[10] The system uses planar graphics, with up to five bitplanes (four in high resolution) allowing 2-, 4-, 8-, 16-, and 32-color screens, from a palette of 4096 colors. Two special graphics modes are also available: Extra HalfBrite, which uses a 6th bitplane as a mask to cut the brightness of any pixel in half (resulting in 32 arbitrary colors plus 32 more colors set at half the value of the first 32), and [[Hold-And-Modify (HAM) which allows all 4096 colors to be used on screen simultaneously.[11] Later revisions of the chipset are PAL/NTSC switchable in software.

The sound chip produces four hardware-mixed channels, two to the left and two to the right, of 8-bit PCM at a sampling frequency of up to 28 kHz. Each hardware channel has its own independent volume level and sampling rate, and can be designated to another channel where it can modulate both volume and frequency using its own output. With DMA disabled it's possible to output with a sampling frequency up to 56 kHz. There's a common trick to output sound with 14-bit precision that can be combined to output 14-bit 56 kHz sound.[12]

The stock system comes with AmigaOS version 1.2 or 1.3 and 512 KiB of chip RAM (150 ns access time), one built-in double-density standard floppy disk drive that is completely programmable and can read 720 KiB IBM PC disks, 880 KiB standard Amiga disks, and up to 984 KiB using custom-formatting drivers.

Despite the lack of Amiga 2000-compatible internal expansion slots, there are many ports and expansion options. There are two DE9M Atari joystick ports for joysticks or mice, stereo audio (RCA connectors 1 V p-p). There is a floppy drive port for daisy-chaining up to three extra floppy disk drives via a DB23F connector.[13] The then-standard RS-232 serial port (DB25M) and Centronics parallel port (DB25F) are also included. The power supply is (+5V, +/-12V).[14] The system displays video in analog RGB 50 Hz PAL or 60 Hz NTSC through a proprietary DB23M connector and in NTSC mode the line frequency is 15,750 Hz HSync for standard video modes, which is compatible with NTSC television and CVBS/RGB video, but out of range for most VGA-compatible monitors, while a multisync monitor is required for some of the higher resolutions. This connection can also be genlocked to an external video signal. The system was bundled with an RF adapter to provide output on televisions with a coaxial RF input, while monochrome composite video is available via an RCA connector (also coaxial). On the left side, behind a plastic cover, there is a Zorro (Zorro I) bus expansion external edge connector with 86 pins. Peripherals such as a hard disk drive can be added via the expansion slot and are configured automatically by the Amiga's AutoConfig standard, so that multiple devices do not conflict with each other. Up to 8 MB of so-called "fast RAM" (memory that can be accessed by the CPU only) can be added using the side expansion slot. This connector is electronically identical with the Amiga 1000's, but swapped on the other side.

The Amiga 500 has a "trap-door" slot on the underside for a RAM upgrade (typically of 512 KiB). This extra RAM is classified as "fast" RAM, but is sometimes referred to as "slow" RAM: due to the design of the expansion bus, it is actually on the chipset bus. Such upgrades usually include a battery-backed real-time clock. All versions of the A500 can have the additional RAM configured as chip RAM by a simple hardware modification, which involves fitting a later model (8372A) Agnus chip. Likewise, all versions of the A500 can be upgraded to 2 MB chip RAM by fitting the 8372B Agnus chip and adding additional memory.

The Amiga 500 also sports an unusual feature for a budget machine, socketed chips, which allow easy replacement of defective chips. The CPU can be directly upgraded on the motherboard to a 68010; or to a 68020, 68030, or 68040 via the side expansion slot; or by removing the CPU and plugging a CPU expansion card into the CPU socket (though this will require opening the computer and voiding any remaining warranty). In fact, all the custom chips can be upgraded to the Amiga Enhanced Chip Set (ECS) versions.

The case is made from ABS plastics which may become brown with time. This may be reversed by using the public-domain chemical mix "Retr0bright", though without a clearcoat to block oxygen, the brown colouring will return.

Technical specifications[edit]

The standard Amiga 500 requires floppies to boot
  • OCS (1.2 & 1.3 models) or ECS (1.3 and 500+ 2.04 models) chipset. ECS revisions of the chipset made PAL/NTSC mode switchable in software.
    • Graphics can be of arbitrary dimensions, resolution and colour depth, even on the same screen.
    • Without using overscan, the graphics can be 320 or 640 pixels wide by 200/256 or 400/512 pixels tall.
    • Planar graphics are used, with up to 5 bitplanes (4 in hires); this allowed 2, 4, 8, 16 and 32 colour screens, from a palette of 4096 colours. Two special graphics modes were also included: Extra HalfBrite, which used a 6th bitplane as a mask that halved the brightness of any colour seen, and Hold-And-Modify (HAM), which allowed all 4096 colours on screen at once.
    • Sound: 4 hardware-mixed channels of 8-bit sound at up to 28 kHz.[15] The hardware channels have independent volumes (65 levels) and sampling rates, and are mixed down to two fully left and fully right stereo outputs. A software controllable low-pass audio filter is also included.
  • 512 KB of chip RAM (150 ns access time).
  • AmigaOS 1.2 or 1.3 (upgradeable up to 3.1.4[16] if 2MB of RAM are installed)
  • One double-density floppy disk drive is built in, which is completely programmable and thus can read 720 KiB IBM PC disks, 880 KiB standard Amiga disks, and up to 984 KiB with custom formatting (such as Klaus Deppich's diskspare.device). Uses 300 rpm (5 rotations/second) and 250 kbit/s.
  • Built-in keyboard.
  • A two-button mouse is included.

Graphics[edit]

  • PAL mode: 320×256, 640×256, 640×512 (interlaced),[17] 704×576 in overscan.
  • NTSC mode: 320×200, 640×200, 640×400 (interlaced),[17] 704×484 in overscan.

Max 6 bpp. The Amiga can show multiple resolution modes at the same time, splitting the screen vertically. An additional mode called Hold-And-Modify (HAM) makes it possible to use 12 bpp over a 3 pixels wide span. This works by letting each pixel position use the previous RGB value and modify one of the red, green or blue values to a new 4-bit value. This will cause some negligible colour artifacts however.

Memory[edit]

Using various expansion techniques, the A500's total RAM can reach up to 138 MiB – 2 MiB Chip RAM, 8 MiB 16-bit Fast RAM, and 128 MiB 32-bit Fast RAM.

Chip RAM[edit]

The stock 512 KiB Chip RAM can be complemented by 512 KiB using a "trapdoor" expansion (Commodore A501 or compatible). While that expansion memory is connected the chip bus, hardware limitations of the stock Agnus chip prevent its use as Chip RAM, only the CPU can access it. Suffering from the same contention limitations as Chip RAM, that memory is known as "Slow RAM" or "Pseudo-fast RAM". Retrofitting a later ECS Agnus and changing the memory-layout jumper allows use of trapdoor RAM as real Chip RAM for a total 1 MiB.

Additionally, several third-party expansions exist with up to 1.8 MiB on the trapdoor board. Using a Gary adapter, that memory is mapped similar to the standard Slow RAM and only usable by the CPU, yet slowed by chipset access.

Furthermore, using an A3000 Agnus on an adapter board, it is possible to expand the Chip RAM to 2 MiB.

Fast RAM[edit]

"Fast" RAM is located on the CPU-side bus. Its access is exclusive to the CPU and not slowed by any chipset access. The side expansion port allows for up to 8 MiB of Zorro-style expansion RAM. Alternatively, a CPU adapter allows for internal expansion.

Accelerator RAM[edit]

Internal or external CPU accelerators often include their own expansion memory. 16-bit CPUs are limited by the 24-bit address space but they can repurpose otherwise unused memory space for their included RAM. 32-bit CPU accelerators aren't limited by 24-bit addressing and can include up to 128 MiB of Fast RAM (and potentially more).

Connectors[edit]

Backside with connectors
The Amiga 520 adapter allowed for an RF modulated output, to be connected to a TV
  • Two DE9M Atari joystick ports for joysticks or mice
  • Stereo audio (RCA connectors 1 V p-p)
  • A floppy drive port (DB23F), for daisy-chaining up to 3 extra floppy disk drives via a DB23F connector[13]
  • A standard RS-232 serial port (DB25M)
  • A parallel port (DB25F)
  • Power inlet (+5 V, +/-12 V)[14]
  • Analogue RGB 50 Hz PAL and 60 Hz NTSC video output, provided on an Amiga-specific DB23M video connector. Can drive video with 15,750 Hz HSync for standard Amiga video modes. This is not compatible with most VGA monitors. A Multisync monitor is required for some higher resolutions. This connection can also be genlocked to an external video signal. An RF adapter (A520) was frequently bundled with the machine to provide output on regular televisions or on composite monitors. A digital 16 colour Red-Green-Blue-Intensity signal is available too on the same connector.
  • Monochrome video via an RCA connector
  • Zorro II bus expansion on the left side behind a plastic cover
  • Trapdoor slot under the machine, for RAM expansion and real-time clock

Expansions[edit]

  • Expansion ports are limited to a side expansion port and a trapdoor expansion on the underside of the machine. The casing can also be opened up (voiding the warranty), all larger chips are socketed rather than being TH/SMD soldered directly to the motherboard, so they can be replaced by hand.
  • The CPU can be upgraded to a Motorola 68010 directly or to a 68020, 68030 or 68040 via the side expansion slot or a CPU socket adapter board.
  • The chip RAM can be upgraded to 1 MB directly on the motherboard, provided a Fat Agnus chip is also installed to support it.
  • Likewise, all the custom chips can be upgraded to the ECS chipset.
  • The A500+ model instead allowed upgrading by 1 MB trapdoor chip RAM without clock, but there was no visible means on board to map any of this as FAST, causing incompatibility with some stubbornly coded programs.
  • There were modification instructions available for the A500 to solder or socket another 512 KB RAM on the board, then run extra address lines to the trapdoor slot to accommodate an additional 1 MB of fast or chip RAM depending on the installed chipset.
  • Up to 8 MB of "fast RAM" can be added via the side expansion slot, even more if an accelerator with a non-EC (without reduced data/address bus) processor and 32-bit RAM is used.
  • Hard drive and other peripherals can be added via the side expansion slot.
  • Several companies provided combined CPU, memory and hard drive upgrades – or provided chainable expansions that extended the bus as they were added – as there is only one side expansion slot.
  • Expansions are configured automatically by AutoConfig software, so multiple pieces of hardware did not conflict with each other.

Diagnostics[edit]

When the computer is powered on a self-diagnostic test is run that will indicates failure with a specific colour:

  1.    Medium green means no chip RAM found or is damaged.
  2.    Red means bad kickstart-ROM.
  3.    Yellow means the CPU has crashed (no trap routine or trying to run bad code) or a bad Zorro expansion card.[18]
  4.    Blue means a custom chip problem (Denise, Paula, or Agnus).
  5.    Light green means CIA problem.
  6.    Light gray means that the CIA might be defective.
  7.     Black and white stripes mean there is a ROM or CIA problem.
  8.    Black-only (no video) means there is no video output.[19]

The keyboard LED uses blink codes:

  1. One blink means the keyboard ROM has a checksum error.
  2. Two blinks means RAM failure.
  3. Three blinks means watchdog timer failure.[19]

Memory map[edit]

Amiga system memory map[20][21]
Address Size in KB Description
0x0000 0000 256.0 Chip RAM
0x0004 0000 256.0 Chip RAM (A1000 option card)
0x0008 0000 512.0 Chip RAM expansion
0x0010 0000 1024.0 Extended Chip RAM for ECS/AGA.
0x0020 0000 8192.0 Primary auto-config space (Fast RAM)
0x00A0 0000 1984.0 Reserved
0x00BF D000 3.8 8520-B (even-byte addresses)
0x00BF E001 3.8 8520-A (odd-byte addresses)
0x00C0 0000 1536.0 Internal expansion memory (pseudo-fast, "slow" RAM on Amiga 500)
0x00D8 0000 256.0 Reserved
0x00DC 0000 64.0 Real time clock
0x00DD 0000 188.0 Reserved
0x00DF F000 4.0 Custom chip registers
0x00E0 0000 512.0 Reserved
0x00E8 0000 64.0 Zorro II auto-config space (before relocation)
0x00E9 0000 448.0 Secondary auto-config space (usually 64K I/O boards)
0x00F0 0000 512.0 512K System ROM (reserved for extended ROM image e.g. CDTV or CD³²)
0x00F8 0000 256.0 256K System ROM (Kickstart 2.04 or higher)
0x00FC 0000 256.0 256K System ROM

Trap-door expansion 501[edit]

An A501 compatible expansion

A popular expansion for the Amiga 500 was the Amiga 501 circuit board that can be installed underneath the computer behind a plastic cover. The expansion contains 512 KiB RAM configured by default as "Slow RAM" or "trap-door RAM" and a battery-backed real-time clock (RTC). The 512 KB trap-door RAM and 512 KB of original chip RAM will result in 1 MB of total memory. By default, the expansion memory is handled and reported by the system as fast memory. However, the RAM is physically connected to Agnus like chip RAM and it is impacted by chip-bus bandwidth contention. Being only accessible by the CPU but as slow as chip RAM, it is commonly being referred to as "Slow RAM". The motherboard can be modified to relocate the trap-door RAM to the chip memory pool, provided a compatible Agnus chip is fitted on the motherboard.

Notable uses[edit]

See also[edit]

References[edit]

  1. ^ Using existing hardware, an A500 can be expanded by an internal CPU board with up to 128 MiB like a DCE Viper 530, 8 MiB external Fast RAM, and 2 MiB Agnus expansion.
  2. ^ "Commodore-Amiga Sales Figures". www.amigahistory.plus.com. Archived from the original on September 27, 2018. Retrieved February 4, 2020.
  3. ^ Gareth Knight. "Commodore-Amiga Sales Figures". www.amigau.com. amigau.com. Archived from the original on May 24, 2009. Retrieved July 24, 2013.
  4. ^ http://www.amigahistory.plus.com/a500batman.html
  5. ^ Gareth Knight (October 21, 2002). "Cartoon Classics Bundles". Amigahistory.co.uk. Retrieved July 24, 2013.
  6. ^ https://archive.org/details/AmigaShopperIssue15Jul92
  7. ^ Gareth Knight. "Commodore History". Amigahistory.co.uk. Retrieved July 24, 2013.
  8. ^ "Low-End Amiga". BYTE. June 1987. p. 52. Retrieved November 5, 2013.
  9. ^ Agnus was enhanced to control up to 1 MB RAM and glue logic was integrated into Gary to reduce costs.
  10. ^ Peck, Robert; Deyl, Susan; Miner, Jay; Raymond, Chris (September 1986). Amiga hardware reference manual. Addison Wesley. p. 72. ISBN 0-201-11077-6.
  11. ^ Peck, Robert; Deyl, Susan; Miner, Jay; Raymond, Chris (September 1986). Amiga hardware reference manual. Addison Wesley. p. 37. ISBN 0-201-11077-6.
  12. ^ "Aminet: mus/play/Play16.lha". aminet.net. November 9, 2003. Archived from the original on March 20, 2020. Retrieved February 16, 2016.
  13. ^ a b "Hi Res Version, Rear of Amiga 500 – 122K". amigahardware.mariomisic.de. 070728 amigahardware.mariomisic.de
  14. ^ a b "Amiga 500/600/1200 Power Connector". www.ntrautanen.fi. Archived from the original on September 27, 2007. Retrieved August 8, 2007. 070808 ntrautanen.fi
  15. ^ "Amiga 500". www.old-computers.com. Archived from the original on March 30, 2010. Retrieved December 15, 2009.
  16. ^ "AmigaOS 3.1.4 on A500". amigax1000.blogspot.com. Retrieved September 3, 2019.
  17. ^ a b http://amiga.lychesis.net/knowledge/ScreenModes.html
  18. ^ abime.net – Question blinking power LED/no screen on Amiga 500 read November 3, 2011
  19. ^ a b amiga.serveftp.net – A3000 Booting Problems read November 3, 2011
  20. ^ Amiga Hardware Reference Manual
  21. ^ "Amiga System Memory Map". www.ntrautanen.fi. Archived from the original on October 24, 2003.