Amiga 1000 - Technical Information

Technical Information

The Amiga 1000 has a Motorola 68000 CPU running at 7.15909 MHz (on NTSC systems) or 7.09379 MHz (PAL systems), precisely double the video color carrier frequency for NTSC or 1.6 times the color carrier frequency for PAL. The system clock timings are derived from the video frequency, which simplifies glue logic and allows the Amiga 1000 to make do with a single crystal. The chipset was designed to synchronize CPU memory access and chipset DMA so the hardware runs in real-time without wait-state delays.

Though most units were sold with an analog RGB monitor, the A1000 also had a built-in composite video output which allowed the computer to be connected directly to monitors other than their standard RGB monitor. The A1000 also had a "TV MOD" output, into which an RF Modulator could be plugged in, allowing connection to a standard TV or VCR.

The original 68000 CPU can be directly replaced with a 68010, which can execute instructions slightly faster than the 68000 but also introduces a small degree of software incompatibility. Third-party CPU upgrades, which mostly fit in the CPU socket, use faster 68020/68881 or 68030/68882 microprocessors and integrated memory. Such upgrades often have the option to revert to 68000 mode for full compatibility. Some boards have a socket to seat the original 68000, whereas the 68030 cards typically come with an on-board 68000.

The original Amiga 1000 is the only model to have 256 kB of Amiga Chip RAM, which can be expanded to 512 kB with the addition of a daughterboard under a cover in the centre front of the machine. RAM may also be upgraded via official and third-party upgrades, with a practical upper limit of about 9 MB of "fast" RAM due to the 68000's 24-bit address bus. This memory is accessible only by the CPU permitting faster code execution as DMA cycles are not shared with the chipset.

The Amiga 1000 features an 86-pin expansion port (electrically identical to the later Amiga 500 expansion port, though the A500's connector is inverted). This port was utilized by third-party expansions such as memory upgrades and SCSI adaptors. These resources are handled by the Amiga AutoConfig standard. Other expansion options were available including a bus expander which provided two Zorro-II slots.