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The Intel MCS-51 (commonly termed 8051) is a single-chip microcontroller (MCU) series developed by Intel in 1980 for use in embedded systems. The architect of the Intel MCS-51 instruction set was John H. Wharton .
A status register, flag register, or condition code register (CCR) is a collection of status flag bits for a processor.Examples of such registers include FLAGS register in the x86 architecture, flags in the program status word (PSW) register in the IBM System/360 architecture through z/Architecture, and the application program status register (APSR) in the ARM Cortex-A architecture.
The zero flag is a single bit flag that is a central feature on most conventional CPU architectures (including x86, ARM, PDP-11, 68000, 6502, and numerous others).It is often stored in a dedicated register, typically called status register or flag register, along with other flags.
In a computer's central processing unit (CPU), the accumulator is a register in which intermediate arithmetic logic unit results are stored.. Without a register like an accumulator, it would be necessary to write the result of each calculation (addition, multiplication, shift, etc.) to cache or main memory, perhaps only to be read right back again for use in the next operation.
The PA-RISC and PICmicro architectures use the carry bit convention, but call their a+not(b)+C operation "subtract with borrow" (SUBB and SUBWFB). The ST6 8-bit microcontrollers are perhaps the most confusing of all. Although they do not have any sort of "subtract with carry" instruction, they do have a carry bit which is set by a subtract ...
Because special registers are closely tied to some special function or status of the microcontroller, they might not be directly writeable by normal instructions (such as adds, moves, etc.). Instead, some special registers in some microcontroller architectures require special instructions to modify them.
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 ...
Keeping the addressing mode specifier bits separate from the opcode operation bits produces an orthogonal instruction set. As the ultimate end of orthogonal design is simply to allow any instruction to use any type of address, implementing orthogonality is often simply a case of adding more wiring between the parts of the processor.
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