Central Air Data Computer

Central Air Data Computer

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The Central Air Data Computer is the integrated flight control system used in the early versions of the US Navy's F-14 Tomcat
F-14 Tomcat
The Grumman F-14 Tomcat is a supersonic, twin-engine, two-seat, variable-sweep wing fighter aircraft. The Tomcat was developed for the United States Navy's Naval Fighter Experimental program following the collapse of the F-111B project...

 fighter. It is notable for its early use of a custom-designed MOS-based LSI chipset, the MP944.

The CADC was designed and built at Garrett AiResearch
Garrett AiResearch
Garrett AiResearch was a manufacturer of turboprop engines and turbochargers, and a pioneer in numerous aerospace technologies. It was previously known as Aircraft Tool and Supply Company, Garrett Supply Company, AiResearch Manufacturing Company, or simply AiResearch...

 by a team led by Steve Geller and Ray Holt
Ray holt
Raymond M. Holt was a pioneering computer designer and businessman in Silicon Valley.From 1968-1970, Holt developed the first microprocessor chip set for Garrett AiResearch's Central Air Data Computer for the F-14 Tomcat....

, and supported by the startup American Microsystems. Design work started in 1968 and was completed in June 1970, beating out a number of electromechanical systems that had also been designed for the F-14.

The CADC consisted of an A-to-D converter
Analog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...

, several quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 pressure sensors, and the MOS-based CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

. Inputs to the system included the primary flight controls, a number of switches, static and dynamic air pressure (for calculating stall points and aircraft speed) and a temperature gauge. The outputs controlled the primary flight controls, wing sweep, the F-14's leading edge "glove", and the flaps.

The MP944 contained six chips used to build the CADC's CPU, all based on a 20-bit fixed-point-fraction two's complement
Two's complement
The two's complement of a binary number is defined as the value obtained by subtracting the number from a large power of two...

 number system. They were the Parallel Multiplier Unit (PMU), the Parallel Divider Unit (PDU), the Random Access Storage (RAS), the Read Only Memory
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...

 (ROM), the Special Logic Function (SLF), and the Steering Logic Unit (SLU). The complete microprocessor system used one PMU, one PDU, one SLF, 3 RASs, 3 SLUs, and 19 ROMs.

Holt wrote an article for Computer Design magazine about the system in 1971, but the Navy classified
Classified information in the United States
The United States government classification system is currently established under Executive Order 13526, the latest in a long series of executive orders on the topic. Issued by President Barack Obama in 2009, Executive Order 13526 replaced earlier executive orders on the topic and modified the...

it, only releasing it in 1998. For this reason the CADC and MP944 remain fairly obscure in spite of their historical importance.