The Signetics 2650, according to Adam Osborne's classic book An Introduction to Microprocessors Vol 2: Some Real Products, was "the most minicomputer-like" of the 8-bit microprocessors.

The manufacturer, Signetics, was not an expert in manufacturing complex MOS chips. They did however bring out a very good development board at a reasonable price, so the chip found use with a limited number of hobbyists, particularly in Australia. 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 many 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 language.

Two types of video game console used the Signetics 2650 or 2650A with the first being consoles based on the 1292 Advanced Programmable Video System and the closely related Interton VC4000, released in Germany in 1976 and 1978 respectively. The second group of consoles were based on the Emerson Arcadia 2001 which was released in 1981 and used a Signetics 2650 running at 3.58 MHz as a CPU and a Signetics 2637 as a video controller.

The processor was also used in the Signetics Instructor 50, which was a small computer designed to teach the use and programmation of the Signetics 2650 CPU.

External links

• Signetics 2650 family CPU World
• Instructor 50 Old-computers.com
• Adaptable Board Computer development system complete with 1 KiB PipBug monitor and 512 bytes of RAM

Microprocessors