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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. [1] [2] Intel's original versions were popular in the 1980s and early 1990s, and enhanced binary compatible derivatives remain ...
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 ...
Computer architectures are often described as n-bit architectures. In the first 3 ⁄ 4 of the 20th century, n is often 12, 18, 24, 30, 36, 48 or 60.In the last 1 ⁄ 3 of the 20th century, n is often 8, 16, or 32, and in the 21st century, n is often 16, 32 or 64, but other sizes have been used (including 6, 39, 128).
A subtract with borrow (SBB) instruction will compute a−b−C = a−(b+C), while a subtract without borrow (SUB) acts as if the borrow bit were clear. The 6800, 680x0, 8051, 8080/Z80, and x86 [2] families (among others) use a borrow bit.
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.
Below is the full 8086/8088 instruction set of Intel (81 instructions total). [2] These instructions are also available in 32-bit mode, in which they operate on 32-bit registers ( eax , ebx , etc.) and values instead of their 16-bit ( ax , bx , etc.) counterparts.
The IBM 704, 709, 704x and 709x store one instruction in each instruction word; IBM numbers the bit from the left as S, 1, ..., 35. Most instructions have one of two formats: Generic S,1-11 12-13 Flag, ignored in some instructions 14-17 unused 18-20 Tag 21-35 Y Index register control, other than TSX S,1-2 Opcode 3-17 Decrement 18-20 Tag 21-35 Y
If x 2 − y 2 is evaluated as ((x × x) − y × y) (following Kahan's suggested notation in which redundant parentheses direct the compiler to round the (x × x) term first) using fused multiply–add, then the result may be negative even when x = y due to the first multiplication discarding low significance bits. This could then lead to an ...