Capricorn (microprocessor)
Encyclopedia
The Capricorn family of microprocessor
s was developed by Hewlett-Packard
in the late 1970s for the HP series 80
scientific microcomputers. Capricorn was first used in the HP-85 desktop BASIC
computer, introduced in January of 1980.
(ALU), a shifter and control logic. One register pair is defined as the program counter, another pair as the stack pointer, and one more pair as an index pointer for internal operations. There is no dedicated accumulator — any general register can be used for ALU results because the register file is designed to allow two read and one write operations at the same time. Any pair of registers can be used as a 16-bit index register.
The ALU can work either in binary
or binary-coded decimal
(BCD) mode. Variable-length instructions let the programmer treat data in the upper 32 registers as entities between one and eight bytes in length — for example, two eight-byte values (e.g. mantissa of a floating-point number) can be added using a single instruction. This feature reduces the number of loops that need to be programmed.
The CPU has an interrupt mechanism with up to 127 vectors. For direct memory access
, the CPU can be halted by an external device.
circuit (4.93×4.01 mm²) in a 28-pin dual in-line package
, with an 8-bit, multiplexed external bus. The CPU chip consumed 330 mW at 625 kHz.
CPU timing is controlled by four non-overlapping clock phases with 200 nanosecond
width and 200 nanosecond spacing, for an overall clock cycle of 1.6 microseconds, equivalent to 625 kHz clock frequency.
The complete system included support chips co-designed with the CPU, such as a dynamic memory controller, keyboard controller with timers, printer controller and CRT controller. A special buffer chip connected to the expansion slots.
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
s was developed by Hewlett-Packard
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...
in the late 1970s for the HP series 80
HP series 80
The Hewlett-Packard series 80 of small scientific desktop computers was introduced in 1980, beginning with the popular HP-85 targeted at engineering and control applications. They provided the capability of the HP 9800 series desktop computers in a smaller package including storage and printer, at...
scientific microcomputers. Capricorn was first used in the HP-85 desktop BASIC
BASIC
BASIC is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use - the name is an acronym from Beginner's All-purpose Symbolic Instruction Code....
computer, introduced in January of 1980.
Architecture
The Capricorn is a microprogrammed CPU containing 64 eight-bit registers, an eight-bit arithmetic logic unitArithmetic logic unit
In computing, an arithmetic logic unit is a digital circuit that performs arithmetic and logical operations.The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers...
(ALU), a shifter and control logic. One register pair is defined as the program counter, another pair as the stack pointer, and one more pair as an index pointer for internal operations. There is no dedicated accumulator — any general register can be used for ALU results because the register file is designed to allow two read and one write operations at the same time. Any pair of registers can be used as a 16-bit index register.
The ALU can work either in binary
Binary numeral system
The binary numeral system, or base-2 number system, represents numeric values using two symbols, 0 and 1. More specifically, the usual base-2 system is a positional notation with a radix of 2...
or binary-coded decimal
Binary-coded decimal
In computing and electronic systems, binary-coded decimal is a digital encoding method for numbers using decimal notation, with each decimal digit represented by its own binary sequence. In BCD, a numeral is usually represented by four bits which, in general, represent the decimal range 0 through 9...
(BCD) mode. Variable-length instructions let the programmer treat data in the upper 32 registers as entities between one and eight bytes in length — for example, two eight-byte values (e.g. mantissa of a floating-point number) can be added using a single instruction. This feature reduces the number of loops that need to be programmed.
The CPU has an interrupt mechanism with up to 127 vectors. For direct memory access
Direct memory access
Direct memory access is a feature of modern computers that allows certain hardware subsystems within the computer to access system memory independently of the central processing unit ....
, the CPU can be halted by an external device.
Implementation
The Capricorn CPU was implemented as a silicon-gate NMOS logicNMOS logic
N-type metal-oxide-semiconductor logic uses n-type metal-oxide-semiconductor field effect transistors to implement logic gates and other digital circuits...
circuit (4.93×4.01 mm²) in a 28-pin dual in-line package
Dual in-line package
In microelectronics, a dual in-line package is an electronic device package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be through-hole mounted to a printed circuit board or inserted in a socket.A DIP is usually referred to as a DIPn, where n is...
, with an 8-bit, multiplexed external bus. The CPU chip consumed 330 mW at 625 kHz.
CPU timing is controlled by four non-overlapping clock phases with 200 nanosecond
Nanosecond
A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns....
width and 200 nanosecond spacing, for an overall clock cycle of 1.6 microseconds, equivalent to 625 kHz clock frequency.
The complete system included support chips co-designed with the CPU, such as a dynamic memory controller, keyboard controller with timers, printer controller and CRT controller. A special buffer chip connected to the expansion slots.