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The RL78 family is an accumulator-based register-bank CISC instruction set architecture (ISA). [2] Although it has eight 8-bit registers or four 16-bit register pairs, essentially all arithmetic operations are performed on a single accumulator (the A register or AX register pair).
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.
Instructions included an address for the operand. For instance, an ADD address instruction would cause the CPU to retrieve the number in memory found at that address and then add it to the value already in the accumulator. This very simple example ISA has a "one-address format" because each instruction includes the address of the data. [4]
In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. [1] A device or program that executes instructions described by that ISA, such as a central processing unit (CPU), is called an implementation of that ISA.
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 ...
Main accumulator extended to 16-bit (C) [34] while keeping 8-bit (A) for compatibility and main registers can now address up to 24-bit (16-bit wide data instruction/24-bit memory address). MeP: 4: 8: Media-embedded processor was a 32-bit processor developed by Toshiba with a modded 8080 instruction set. Only the A, B, C, and D registers are ...
On an accumulator-based architecture machine, this may be a dedicated register. On a machine with multiple general-purpose registers , it may be a register that is reserved by convention, such as on the IBM System/360 through z/Architecture architecture and RISC architectures, or it may be a register that procedure call and return instructions ...
Diagram of the Intel Core 2 microarchitecture. In electronics, computer science and computer engineering, microarchitecture, also called computer organization and sometimes abbreviated as μarch or uarch, is the way a given instruction set architecture (ISA) is implemented in a particular processor. [1]