Signetics 2650A

The Signetics 2650, was a very early (1975) 8-bit microprocessor. According to Adam Osborne's classic book An Introduction to Microprocessors Vol 2: Some Real Products, it was "the most minicomputer-like" of the microprocessors available at the time.

Signetics sold development boards e.g. the PC1500 "Adaptable Board Computer", ranging in price from $AUD 165 to $AUD 400. The chip by itself sold for around $AUD 20. Several hardware construction projects and programming articles were published in magazines such as Electronics Australia and Elektor and related kits were sold by electronics stores. These factors led to its use by a number of hobbyists, particularly in Australia where a user group was formed.

The chip contained 7 8-bit general purpose registers, although only 4 were visible at any time. It was limited to a 15-bit address space (thereby addressing a maximum of 32KB of memory), since the upper bit of a 16-bit memory reference was reserved to indicate that the indirect memory addressing mode was to be used (a minicomputer-like feature).

While there were nine different addressing modes, the lack of any 16-bit registers and the 15-bit address space prevented widespread use. Despite this, an operating system ("2650 DOS") was available, along with a BASIC interpreter, and many games of the Hunt the Wumpus style. Most programs were written in assembly languages. Other manufacturers who produced compatible chips included Harris, Intersil, Synertek

Machines that used the 2650

• Emerson Arcadia 2001 console family
• Interton VC 4000 console family (c. 1978);
• Elektor TV Games Computer (1979);
• Signetics Instructor 50 trainer (c. 1978);
• Central Data 2650 computer (1977);
• Malzak 1 and 2 coin-ops (c. 1980);
• Astro Wars and Galaxia coin-ops (1979-1980);
• Chaos 2 computer (1983)
• Dolphin computer (1979)

Emulation

• MESS
• MAME
• AmiArcadia and WinArcadia