The Rockwell PPS-4, short for "Parallel Processing System, 4-bit", was an early

4-bit 4-bit computing is the use of computer architectures in which integer (computer science), integers and other data (computer science), data units are 4 bits wide. 4-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures a ...

microprocessor A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...

from

Rockwell International Rockwell International was a major American manufacturing conglomerate (company), conglomerate. It was involved in aircraft, the space industry, defense and commercial electronics, components in the automotive industry, printing presses, avioni ...

, released in late 1972. Although practically unknown today, the PPS series was widely used in calculators, games and toys, and other embedded applications. Updated versions continued to be produced into the 1980s. The original version was implemented in a three-chip set, consisting of the CPU, a clock generator, and a user ROM. In 1975, the clock generator was integrated to produce the PPS-4/2 with a variety of ROM and RAM support chips. In 1976, the PPS-4/1 added user-customized ROM to produce a single-chip solution, running at a lower speed. The release of the PPS-4/1 coincided with the release of the Rockwell PPS-8, a more advanced

8-bit In computer architecture, 8-bit integers or other data units are those that are 8 bits wide (1 octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data bu ...

processor. Support chips released for the PPS-8 also worked with the PPS-4/1. These versions of the lineup continued to be produced into the 1980s. The PPS-8, however, was abandoned shortly after its introduction as more advanced 8-bit processors entered the market.

Description

The PPS-4 was built on a

metal gate A metal gate, in the context of a lateral metal–oxide–semiconductor (MOS) stack, is the gate electrode separated by an oxide from the transistor's channel – the gate material is made from a metal. In most MOS transistors since about the mid- ...

process, compared to the contemporary

Intel 4004 The Intel 4004 was part of the 4 chip MCS-4 micro computer set, released by the Intel, Intel Corporation in November 1971; the 4004 being part of the first commercially marketed microprocessor chipset, and the first in a long line of List of I ...

which was based on the more advanced

silicon gate In semiconductor electronics fabrication technology, a self-aligned gate is a transistor manufacturing approach whereby the gate electrode of a MOSFET (metal–oxide–semiconductor field-effect transistor) is used as a mask for the doping of the ...

PMOS logic PMOS or pMOS logic, from p-channel metal–oxide–semiconductor, is a family of digital circuits based on p-channel, enhancement mode metal–oxide–semiconductor field-effect transistors (MOSFETs). In the late 1960s and early 1970s, PMOS ...

process. This required large amounts of power; it ran on a -17 VDC power supply while running at only 256 kHz, whereas the 4004 ran at 750 kHz on a 15 VDC supply. The CPU, part number 10660, was packaged in a 42-pin

quad in-line package QUaD, an acronym for QUEST at DASI, was a ground-based cosmic microwave background (CMB) Polarization (waves), polarization experiment at the South Pole. QUEST (Q and U Extragalactic Sub-mm Telescope) was the original name attributed to the bolome ...

. The pins included a 12-pin

address bus In computer architecture, a bus (historically also called a data highway or databus) is a communication system that transfers data between components inside a computer or between computers. It encompasses both hardware (e.g., wires, optical ...

, 8-pin

data bus In computer architecture, a bus (historically also called a data highway or databus) is a communication system that transfers data between components inside a computer or between computers. It encompasses both hardware (e.g., wires, optical ...

and three 4-pin

input/output In computing, input/output (I/O, i/o, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, such as another computer system, peripherals, or a human operator. Inputs a ...

ports that could be combined in different ways. Power supply and clock signals took up the rest of its 42 pins. PPS-4's separate data and address buses meant it could read an 8-bit instruction in a single cycle. In contrast, the 16-pin 4004 had 4-bit data and address buses, meaning specifying a 12-bit address required external latches and several cycles to specify the address and then read an instruction. This meant the PPS-4 performed at roughly the same overall speed as the 4004 despite running at the clock speed. A complete system used the 10660 CPU, the 10706 clock generator in a 10-pin TO-5 package, and one of a variety of ROM or RAM chips. The clock was four-phase and based on a standard

NTSC NTSC (from National Television System Committee) is the first American standard for analog television, published and adopted in 1941. In 1961, it was assigned the designation System M. It is also known as EIA standard 170. In 1953, a second ...

crystal due to their widespread availability. The PPS-4/2 was introduced in the autumn of 1975, combining the clock chip onto the die and reducing the system to two chips, the 11660 CPU and a ROM or RAM. It also had a built-in

LED A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresp ...

controller. This would normally be used with the Memory/IO System chip, which combined 2 KB of ROM, 128 bytes of RAM, and 16 serial ports that could be combined in various ways. The PPS-4/1 followed in early 1976, moving at last to a PMOS process, while most other companies had since moved to the new

NMOS logic NMOS or nMOS logic (from N-type metal–oxide–semiconductor) uses n-type (-) MOSFETs (metal–oxide–semiconductor field-effect transistors) to implement logic gates and other digital circuits. NMOS transistors operate by creating an inv ...

. This was designed to work with the recently released PPS-8, which also used the PMOS process. The two were designed to work with a common set of interface chips. A wide variety of PPS-4/1 models were produced, with different amounts of RAM, ROM and I/O ports build into the die. These versions ran much slower than the original models, between 40 and 100 kHz.

Notes

References

Citations

Bibliography

* * * * {{cite tech report , publisher=Rockwell International , title=PPS 4/2 Two-Chip Microcomputer System , date=1975 , url=https://en.wikichip.org/w/images/2/25/rockwell_pps-4-2_manual.pdf Computer-related introductions in 1972 4-bit microprocessors