Signetics 2650

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Signetics 2650AI

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 a development board, (the "Adaptable Board Computer") 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. The first being the consoles based on the 1292 Advanced Programmable Video System and the closely related Interton VC4000. Those were 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 which 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 programming of the Signetics 2650 CPU.

[edit] Second sources

Signetics was sold to Valvo, (the vacuum tube manufacturing sister company of Philips) and the 2650 was later incorporated into the Philips Semiconductors line. They made a version of the 2650 called the MAB 2650 A.

The most well known licensed copy of the Signetics/Philips 2650 was the 2650-P-02 from Synertek.

Other producers of licensed copies of the chip were Harris and Intersil.

[edit] Peripheral Chips

The 2650 came with a full complement of peripheral chips:

2636 Programmable Video Interface
2637 Universal Video Interface
2651 Programmable Communication Interface
2652 Multi-Protocol Communications Circuit (incl. Synchronous Data Link Control (SDLC))
2653 Polynomial Generator / Checker
2655 Programmable Peripheral Interface
2657 Direct Memory Access
2656 System Memory Interface
2661 Programmable Communication Interface
2670 Display Character and Graphics Generator
2671 Programmable Keyboard and Communications Controller
2672 Programmable Video Timing Controller
2673 Video Attributes Controller

Many of these peripheral chips were designed so they could also be used with other microprocessor, for example the datasheet of the 2672 suggests using it with an Intel 8048 microcontroller.

Descendants of the 2651/2661 serial communications chips are still sold as the Philips SC26 series.