Microsequencer

In computer architecture and engineering, a sequencer or microsequencer generates the addresses used to step through the microprogram of a control store. It is used as a part of the control unit of a CPU or as a stand-alone generator for address ranges. Usually the addresses are generated by some combination of a counter, a field from a microinstruction, and some subset of the instruction register. A counter is used for the typical case, that the next microinstruction is the one to execute. A field from the microinstruction is used for jumps, or other logic. Since CPUs implement an instruction set, it's very useful to be able to decode the instruction's bits directly into the sequencer, to select a set of microinstructions to perform a CPU's instructions. Most modern CISC processors use a combination of pipelined logic to process lower complexity opcodes which can be completed in one clock cycle, and microcode to implement ones that take multiple clock cycles to complete. One of the first integrated microcoded processors was the IBM PALM Processor, which emulated all of the processor's instruction in microcode and was used on the IBM 5100, one of the first personal computers. Recent examples of similar open-sourced microsequencer-based processors are the MicroCore Labs MCL86, MCL51 , and MCL65 cores which emulate the Intel 8086/8088, 8051 and MOS 6502 instruction sets entirely in microcode. The Digital Scientific Corp. Meta 4 Series 16 computer system was a user-microprogrammable system first available in 1970. Branches in the microcode sequence occur in one of three ways. A branch microinstruction specifies the address of the next instruction, either conditionally or unconditionally. The logical index (IX) option causes the 16-bit Link register to be logical ORed into the branch address, thus providing a simple indexed branch capability. All the arithmetic/logical instructions allow the jump (J) modifier, which redirects execution to the microinstruction addressed by the Link register.

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Microsequencer

Computer

A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These programs enable computers to perform a wide range of tasks. A computer system is a nominally complete computer that includes the hardware, operating system (main software), and peripheral equipment needed and used for full operation.

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A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components. A computer program in its human-readable form is called source code. Source code needs another computer program to execute because computers can only execute their native machine instructions. Therefore, source code may be translated to machine instructions using the language's compiler.

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