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Though the multiply instruction became common with the 16-bit generation, [4] at least two 8-bit processors have a multiply instruction: the Motorola 6809, introduced in 1978, [5] and Intel MCS-51 family, developed in 1980, and later the modern Atmel AVR 8-bit microprocessors present in the ATMega, ATTiny and ATXMega microcontrollers.
An 8-bit register can store 2 8 different values. The range of integer values that can be stored in 8 bits depends on the integer representation used. With the two most common representations, the range is 0 through 255 (2 8 − 1) for representation as an binary number, and −128 (−1 × 2 7) through 127 (2 7 − 1) for representation as two's complement.
The first computer to have multiple parallel discrete single-bit ALU circuits was the 1951 Whirlwind I, which employed sixteen such "math units" to enable it to operate on 16-bit words. In 1967, Fairchild introduced the first ALU-like device implemented as an integrated circuit, the Fairchild 3800, consisting of an eight-bit arithmetic unit ...
It is performed by reading the binary number from left to right, doubling if the next bit is zero, and doubling and adding one if the next bit is one. [5] In the example above, 11110011, the thought process would be: "one, three, seven, fifteen, thirty, sixty, one hundred twenty-one, two hundred forty-three", the same result as that obtained above.
The circuit produces a two-bit output. Output carry and sum are typically represented by the signals and , where the sum equals +. The full adder is usually a component in a cascade of adders, which add 8, 16, 32, etc. bit binary numbers.
An arithmetic logic unit (ALU) capable of adding and subtracting 8-bit 2's complement integers from registers A and B. This module also has a flags register with two possible flags (Z and C). Z stands for "zero," and is activated if the ALU outputs zero. C stands for "carry," and is activated if the ALU produces a carry-out bit.
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The Zilog eZ80 is an 8-bit microprocessor designed by Zilog as an updated version of the company's first product, the highly-successful Zilog Z80. The eZ80 is binary compatible with the Z80, but operating almost three times faster at the same clock frequency .