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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.
Two-operand instructions by default write to the accumulator, and use an M suffix to indicate a memory destination.) In addition to the different opcode assignment, there are semantic differences in a few instructions: The subtract instructions subtract the operand from the accumulator, while Microchip's subtract instructions do the reverse.
This is done by defining a series of state-components, each with a size and offset within a given save area, and each corresponding to a subset of the state needed for one CPU extension or another. The EAX=0Dh CPUID leaf is used to provide information about which state-components the CPU supports and what their sizes/offsets are, so that the OS ...
[5]: 7, line 2 The basis of 78K Family is an accumulator-based register-bank CISC architecture. 78K is a single-chip microcontroller, which usually integrates; program ROM, data RAM, serial interfaces, timers, I/O ports, an A/D converter, an interrupt controller, and a CPU core, on one die. [6] [7]: 412
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.
The 6100 is a 12-bit CPU that closely emulates the PDP-8 (See PDP-8 for a more complete discussion). It has three primary registers: PC (program counter), 12-bit AC (accumulator), and MQ (Multiplier Quotient). All two-operand instructions read the AC and MQ and write back to the AC.
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