Acorn Atom

The Acorn Atom was released in March 1980, as was available as a kit or assembled.

The Acorn Atom has a 1 MHz 6502 CPU. The minimum system has 2K RAM and 8K ROM. The 2K RAM is split 0.5K for program memory, 0.5K video RAM and 1K page zero, page zero is used by the OS, CPU stack and BASIC variables. The memory can be expanded to 12K RAM, split 5K for programs, 1K page zero and 6K for high resolution graphics (if hi resolution graphics are not used then an additional 5 ½K is available for programs.

The Acorn Atom has a Motorola MC6847 video chip which allows text (32X16 characters) or 2 colour graphics (upto 256 x 192 monochrome). It can be connected to a TV or, with modifications, a monitor. A PAL colour graphics card was also available. A 6522 VIA controls the serial and parallel ports. An INS8255 PPI drives the cassette interface and keyboard.

External Ports

The Atom had a range of interface ports on the rear of the chassis

• Expansion Bus
• VIA Printer I/O
• Video out
• DC In (8V from an external PSU)
• Tape I/O
• UHF TV out

Internal Upgrades

The basic Atom could be expanded with a number of additional components

• Expand the lower text space to 5K, in increments of 1K, this is used for BASIC programs.
• Expand the Video Graphics RAM from 1K to 5K.
• 4Kb Floating Point ROM
• 4Kb Utility ROM, this can be any application.
• 6522 VIA
• Centronics printer port (requires 6522 VIA installed)
• 64-way connector for the Acorn bus and the bus buffers which allow external interface cards to be used with the Atom.
• Eurocard extensions, Any of the Acorn Eurocards can be used with the Atom, including an Econet interface to network the Atom.

Other extension boards can be fittted to PL8