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With a 12 MHz clock frequency, the 8051 could thus execute 1 million one-cycle instructions per second or 500,000 two-cycle instructions per second. Enhanced 8051 cores are now commonly used which run at six, four, two, or even one clock per machine cycle (denoted "1T") and have clock frequencies of up to 100 MHz, thus being capable of an even ...
The 8-bit immediate group grows to 6 instructions by adding ADDLW and RETLW. The latter is moved out of the control transfer group, allowing a full 10-bit address in the CALL instruction. The ALU operations group gains add/subtract with carry (ADCWF, SUBBWF) instructions (7-bit operands).
The 8051 microcontroller has two, a primary accumulator and a secondary accumulator, where the second is used by instructions only when multiplying (MUL AB) or dividing (DIV AB); the former splits the 16-bit result between the two 8-bit accumulators, whereas the latter stores the quotient on the primary accumulator A and the remainder in the ...
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 ...
Arithmetic and logical instructions set some or all of the flags, and conditional jump instructions take variable action based on the value of certain flags. For example, jz (Jump if Zero), jc (Jump if Carry), and jo (Jump if Overflow) depend on specific flags. Other conditional jumps test combinations of several flags.
Registers are normally measured by the number of bits they can hold, for example, an 8-bit register, 32-bit register, 64-bit register, 128-bit register, or more.In some instruction sets, the registers can operate in various modes, breaking down their storage memory into smaller parts (32-bit into four 8-bit ones, for instance) to which multiple data (vector, or one-dimensional array of data ...
The IBM System/360 has a 32-bit architecture with 16 general-purpose registers, but most of the System/360 implementations use hardware that implements a much simpler underlying microarchitecture; for example, the System/360 Model 30 has 8-bit data paths to the arithmetic logic unit (ALU) and main memory and implemented the general-purpose ...
There are 32 general-purpose 8-bit registers, R0–R31. All arithmetic and logic operations operate on those registers; only load and store instructions access RAM. A limited number of instructions operate on 16-bit register pairs. The lower-numbered register of the pair holds the least significant bits and must be even-numbered.