Amiga 500


The Amiga 500, also known as the A500, is the first low-end Commodore Amiga 16/32-bit multimedia home/personal computer. It was announced at the winter Consumer Electronics Show in January 1987at the same time as the high-end Amiga 2000and competed directly against the Atari 520ST. Before it shipped Commodore suggested a list price of without a monitor. At delivery in October 1987 Commodore announced that the machine would carry a list price.
In Europe the Amiga 500 was released in May 1987. In the Netherlands it was available from April 1987 for a list price of 1499 HFL.
The Amiga 500 represents a return to Commodore's roots by being sold in the same mass retail outlets as the Commodore 64to which it was a spiritual successoras opposed to the computer-store-only Amiga 1000, as well as being another computer whose keyboard is included in the same case.
The original Amiga 500 proved to be Commodore's best-selling Amiga model, enjoying particular success in Europe. Although popular with hobbyists, arguably its most widespread use was as a gaming machine, where its advanced graphics and sound were of significant benefit. It has been claimed that over 6 million A500s were sold worldwide, however, according to Commodore UK, the entire sales of all Amigas in both Europe and the USA were 4-5 million.

Releases

In October 1989, the Amiga 500 dropped its price from £499 to £399 and was bundled with the Batman Pack in the United Kingdom which included the games Batman, F/A-18 Interceptor, The New Zealand Story and the bitmap graphics editor, Deluxe Paint 2. Also included was the Commodore A520 RF Modulator, an adaptor which allowed the A500 to be used with a conventional CRT television set, via its RF antenna socket.
In late 1991, an enhanced model known as the Amiga 500 Plus replaced the original 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'.
The Amiga 500 series was discontinued in June 1992 and replaced by the similarly specified and priced Amiga 600, although this new machine had originally been intended as a much cheaper model, which would have been the A300. In late 1992, Commodore released the "next-generation" Amiga 1200, a machine closer in concept to the original Amiga 500, but featuring significant technical improvements. Despite this, neither the A1200 nor the A600 replicated the commercial success of its predecessor, as by this time, the popular market was definitively shifting from the home computer platforms of the past to commodity Wintel PCs and the new "low-cost" Macintosh Classic, LC and IIsi models.

Description

Outwardly resembling the Commodore 128 and codenamed "Rock Lobster" during development, the Amiga 500 houses the keyboard and CPU in one shell, unlike the Amiga 1000. It utilizes a Motorola 68000 microprocessor running at or . 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. So graphics can be displayed in multiple resolutions and color depths, even on the same screen. Resolutions vary from 320×200 to 640×400 for NTSC and 320×256 to 640×512 for PAL The system uses planar graphics, with up to five bitplanes 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, and which allows all 4096 colors to be used on screen simultaneously. 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. 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. There's a common trick to output sound with 14-bit precision that can be combined to output 14-bit sound.
The stock system comes with AmigaOS version 1.2 or 1.3 and of chip RAM, one built-in double-density standard floppy disk drive that is completely programmable and can read IBM PC disks, standard Amiga disks, and up to 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. There is a floppy drive port for daisy-chaining up to three extra floppy disk drives via a DB23F connector. The then-standard RS-232 serial port and Centronics parallel port are also included. The power supply is.
The system displays video in analog RGB PAL or NTSC through a proprietary DB23M connector and in NTSC mode the line frequency is 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. There is also a Zorro bus expansion on the left side. 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 of so-called "fast RAM" 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. 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 Agnus chip. Likewise, all versions of the A500 can be upgraded to chip RAM by fitting the 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. In fact, all the custom chips can be upgraded to the Amiga Enhanced Chip Set 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.
Whenever the computer is powered on a self-diagnostic test is run that will show any failure with a specific colour where medium green means no chip RAM found or is damaged, red means bad kickstart-ROM, yellow means the CPU has crashed or a bad Zorro expansion card.
Blue means custom chip problem,
means CIA problem.
Stopping on means that the CIA might be defective. mean there is a ROM or CIA problem, while
black only means there is no video output.
The keyboard LED uses blink codes: one blink means the keyboard ROM has a checksum error, two blinks means RAM failure, three blinks means watchdog timer failure. Using Caps Lock key and getting a response means CIA and the CPU works. There is no guarantee that every blinking state or color is accurate. Remember when the diagnostic codes are triggered it means the computer has some kind of fault and it can easily mis-interpret the fault and give false readings. For example, if the screen flashes green it can mean the Agnus is bad, the Agnus socket is bad, the logic connected to the Agnus is bad, the logic connected to the CPU is bad, the logic connected to the RAM is bad, a connection between CPU and/or logic and/or Agnus and/or Chip RAM is bad and/or some/all of the chip RAM is faulty etc. etc. Many of the issues with Amigas are caused by damage from corrosion or poor repair skills, especially the A500+ which has a Ni-Cad battery fitted and is always corroded if the battery has not been removed. Likewise a corroded battery on an A501 can cause faults on the A500 motherboard if the corrosion is very bad and has spread to the motherboard. The self-test chip RAM check is very brief and simplistic and all the other tests are minimalistic to minimize the start-up time so there is no guarantee that any of the diagnostic colours are 100% accurate.

Technical specifications

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 makes it possible to utilize over a 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.

Connectors

Trap-door expansion 501

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 RAM configured by default as "Slow RAM" or "trap-door RAM" and a battery-backed real-time clock. 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