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It is primarily used to support binary-coded decimal (BCD) arithmetic. The Auxiliary Carry flag is set (to 1) if during an " add " operation there is a carry from the low nibble (lowest four bits) to the high nibble (upper four bits), or a borrow from the high nibble to the low nibble, in the low-order 8-bit portion, during a subtraction.
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. [1] [2] Intel's original versions were popular in the 1980s and early 1990s, and enhanced binary compatible derivatives remain ...
Instructions which write to the entire flags register: POPF, IRET, interrupts, or any other instruction which causes a hardware task switch. The parity flag is tested by conditional jump instructions; the JP instruction jumps to the given target when the parity flag is set and the JNP instruction jumps if it is not set.
The FLAGS register is the status register that contains the current state of an x86 CPU.The size and meanings of the flag bits are architecture dependent. It usually reflects the result of arithmetic operations as well as information about restrictions placed on the CPU operation at the current time.
In computer processors, the carry flag (usually indicated as the C flag) is a single bit in a system status register/flag register used to indicate when an arithmetic carry or borrow has been generated out of the most significant arithmetic logic unit (ALU) bit position.
C = A+B needs two instructions. RISC — arithmetic instructions use registers only, so explicit 2-operand load/store instructions are needed: load a,reg1; load b,reg2; add reg1+reg2->reg3; store reg3,c; C = A+B needs four instructions. Unlike 2-operand or 1-operand, this leaves all three values a, b, and c in registers available for further ...
An instruction set architecture (ISA) is an abstract model of a computer, also referred to as computer architecture.A realization of an ISA is called an implementation.An ISA permits multiple implementations that may vary in performance, physical size, and monetary cost (among other things); because the ISA serves as the interface between software and hardware.
Arithmetic and logical instructions were mostly performed against values in memory as opposed to internal registers. As a result, many instructions required a two-byte (16-bit) location to memory. Given that opcodes on these processors were only one byte (8 bits) in length, memory addresses could make up a significant part of code size.