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Signetics 2650
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Signetics 2650
The Signetics 2650 was an 8-bit microprocessor introduced in July 1975. According to Adam Osborne's book An Introduction to Microprocessors Vol 2: Some Real Products, it was "the most minicomputer-like" of the microprocessors available at the time. A combination of missing features and odd memory access limited its appeal, and the system saw little use in the market.
In 1972, Signetics' Jack Curtis hired John Kessler of IBM to lead the design of a new single-chip CPU intended to compete with minicomputer systems. Kessler selected the IBM 1130 as the model for the new design. The 1130, released in 1965, was a 16-bit minicomputer that shared many design features with other minis of the era.
While Kessler designed the architecture, Kent Andreas laid out the CPU using a recently developed ion implantation NMOS process. In contrast to the far more common PMOS process of the era, NMOS used less power and dissipated less heat. This allowed the chip to be run at higher speeds than PMOS CPU designs, and the first 2650's ran at the same 1.25 MHz speed as the contemporary models of the 1130.
When it was designed in 1972, the 2650 was among the most advanced designs on the market, easily outperforming and out-featuring the Intel 4004 and 8008 of the same era. Despite this, the design was not released to production. At the time, Signetics was heavily involved with Dolby Laboratories, developing integrated circuits that implemented Dolby's suite of noise-reduction systems. Production of the 2650 was pushed back, and the CPU was not formally introduced until July 1975. By 1975, several new CPUs had been introduced, designed from the start to be 8-bit machines rather than mimicking an older design, and the 2650's advantages were no longer as compelling.
In 1975, Philips purchased Signetics, and from that point versions of the 2650 can be found with both Signetics or Philips branding.
In March 1976, Signetics reached a second-source agreement with Advanced Memory Systems (AMS). At that time, most CPU firms were very small and no one would buy a design from a company that might go bankrupt. Second-sourcing was an important guarantee that the design would remain available in this eventuality. AMS was already acting as a second-source for the RCA 1802, an advanced CMOS design. The NMOS 2650 was seen as a useful adjunct that would not directly compete with the 1802. Unfortunately, in November AMS was purchased by Intersil, who had their own Intersil 6100, a single-chip version of the PDP-8 mini. Intersil dropped production of the 2650.
Signetics tried again with National Semiconductor in 1977, who planned to introduce versions in the last quarter of the year. For unknown reasons, this appears to have never happened, and only a single example of an NS version, from France, has ever been found.
Signetics continued the development of the 2650, introducing two new models in 1977. The 2650A was a reworked version of the original layout intended to improve yield, and thus reduce cost. Speed remained unchanged at 1.25 MHz for the base model and 2 MHz for the -1 versions. The 2650B was based on the A, added two new instructions, and improved the performance of a number of existing instructions.
Hub AI
Signetics 2650 AI simulator
(@Signetics 2650_simulator)
Signetics 2650
The Signetics 2650 was an 8-bit microprocessor introduced in July 1975. According to Adam Osborne's book An Introduction to Microprocessors Vol 2: Some Real Products, it was "the most minicomputer-like" of the microprocessors available at the time. A combination of missing features and odd memory access limited its appeal, and the system saw little use in the market.
In 1972, Signetics' Jack Curtis hired John Kessler of IBM to lead the design of a new single-chip CPU intended to compete with minicomputer systems. Kessler selected the IBM 1130 as the model for the new design. The 1130, released in 1965, was a 16-bit minicomputer that shared many design features with other minis of the era.
While Kessler designed the architecture, Kent Andreas laid out the CPU using a recently developed ion implantation NMOS process. In contrast to the far more common PMOS process of the era, NMOS used less power and dissipated less heat. This allowed the chip to be run at higher speeds than PMOS CPU designs, and the first 2650's ran at the same 1.25 MHz speed as the contemporary models of the 1130.
When it was designed in 1972, the 2650 was among the most advanced designs on the market, easily outperforming and out-featuring the Intel 4004 and 8008 of the same era. Despite this, the design was not released to production. At the time, Signetics was heavily involved with Dolby Laboratories, developing integrated circuits that implemented Dolby's suite of noise-reduction systems. Production of the 2650 was pushed back, and the CPU was not formally introduced until July 1975. By 1975, several new CPUs had been introduced, designed from the start to be 8-bit machines rather than mimicking an older design, and the 2650's advantages were no longer as compelling.
In 1975, Philips purchased Signetics, and from that point versions of the 2650 can be found with both Signetics or Philips branding.
In March 1976, Signetics reached a second-source agreement with Advanced Memory Systems (AMS). At that time, most CPU firms were very small and no one would buy a design from a company that might go bankrupt. Second-sourcing was an important guarantee that the design would remain available in this eventuality. AMS was already acting as a second-source for the RCA 1802, an advanced CMOS design. The NMOS 2650 was seen as a useful adjunct that would not directly compete with the 1802. Unfortunately, in November AMS was purchased by Intersil, who had their own Intersil 6100, a single-chip version of the PDP-8 mini. Intersil dropped production of the 2650.
Signetics tried again with National Semiconductor in 1977, who planned to introduce versions in the last quarter of the year. For unknown reasons, this appears to have never happened, and only a single example of an NS version, from France, has ever been found.
Signetics continued the development of the 2650, introducing two new models in 1977. The 2650A was a reworked version of the original layout intended to improve yield, and thus reduce cost. Speed remained unchanged at 1.25 MHz for the base model and 2 MHz for the -1 versions. The 2650B was based on the A, added two new instructions, and improved the performance of a number of existing instructions.
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