The Capricorn family of microprocessors 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 1980. Steve Wozniak was inspired to build the Apple to be a computer like the HP 9830, and in 1976, he offered HP rights to the Apple computer. He was turned down and was given a release. When the calculator division started an 8-bit computer project called Capricorn, he left for Apple when he wasn't allowed to work on that project.[1][2]
The Capricorn is a microprogrammed CPU containing 64 eight-bit registers, an eight-bit arithmetic logic unit (ALU), a shifter and control logic. The 64 registers are split by boundaries. There is a boundary every two bytes for the first 32 registers and one boundary per 8 bytes for the remaining 32 registers. Each low-level instruction modifies data beginning at the register addressed up to the next boundary. The design results in very compact code. It was up to the coder to access and modify between one and eight bytes using only one CPU instruction.
The first 32 registers are often used for address manipulation. The remaining 32 registers are used for floating point operations. Because there are four sets of eight byte boundary registers (32-63) most floating point operations are done using only registers without any memory access. Six of the first 32 registers are reserved by hardware for use as special-purpose registers: 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 up to two read and one write operations for the first 32 registers and up to eight read and one write operations for the remaining 32 registers 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.
Implementationedit
The Capricorn CPU was implemented as a silicon-gate NMOS logic circuit (4.93×4.01 mm) 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.
Referencesedit
Lynch, Todd R. (August 1980). (PDF). Hewlett-Packard Journal. 31 (8): 16–22. Archived from the original (PDF) on 2019-06-14. Retrieved 2016-07-22.
Mikkelsen, Tim. . Archived from the original on 2009-12-14. Retrieved 2010-02-12.
Notesedit
^Williams, Gregg; Moore, Rob (December 1984). "An Interview with Steve Wozniak". Byte.
capricorn, microprocessor, capricorn, family, microprocessors, developed, hewlett, packard, late, 1970s, series, scientific, microcomputers, capricorn, first, used, desktop, basic, computer, introduced, january, 1980, steve, wozniak, inspired, build, apple, co. The Capricorn family of microprocessors 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 1980 Steve Wozniak was inspired to build the Apple to be a computer like the HP 9830 and in 1976 he offered HP rights to the Apple computer He was turned down and was given a release When the calculator division started an 8 bit computer project called Capricorn he left for Apple when he wasn t allowed to work on that project 1 2 Contents 1 Architecture 2 Implementation 3 References 4 NotesArchitecture editSource 3 The Capricorn is a microprogrammed CPU containing 64 eight bit registers an eight bit arithmetic logic unit ALU a shifter and control logic The 64 registers are split by boundaries There is a boundary every two bytes for the first 32 registers and one boundary per 8 bytes for the remaining 32 registers Each low level instruction modifies data beginning at the register addressed up to the next boundary The design results in very compact code It was up to the coder to access and modify between one and eight bytes using only one CPU instruction The first 32 registers are often used for address manipulation The remaining 32 registers are used for floating point operations Because there are four sets of eight byte boundary registers 32 63 most floating point operations are done using only registers without any memory access Six of the first 32 registers are reserved by hardware for use as special purpose registers 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 up to two read and one write operations for the first 32 registers and up to eight read and one write operations for the remaining 32 registers 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 Implementation editThe Capricorn CPU was implemented as a silicon gate NMOS logic circuit 4 93 4 01 mm 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 References editLynch Todd R August 1980 A Custom LSI Approach to a Personal Computer PDF Hewlett Packard Journal 31 8 16 22 Archived from the original PDF on 2019 06 14 Retrieved 2016 07 22 Mikkelsen Tim What is the cpu for HP 87 Archived from the original on 2009 12 14 Retrieved 2010 02 12 Notes edit Williams Gregg Moore Rob December 1984 An Interview with Steve Wozniak Byte Old Computers HP 85 Capricorn CPU documentation a subset of the HP85 assembler ROM manual PDF Archived PDF from the original on 2018 11 06 Retrieved 2020 02 06 nbsp This microcomputer or microprocessor related article is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Capricorn microprocessor amp oldid 1185025778, wikipedia, wiki, book, books, library,
