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Each mnemonic maps directly to a machine instruction code, known as an opcode. Some mnemonics map to more than one opcode, however the instruction's operand types will determine which specific opcode will be generated.
Mnemonic means memory aid.Instruction mnemonics are easy to remember short alphanumeric strings that stand for op codes.Op codes are numbers that are understood by the computer and command it to perform various operations. They are usually inherently difficult for humans to remember.
Mnemonics is a method of remembering things by associascation. Hexadecimal is a number system. 0-9 are as usual and then a(10) b(11) c(12) d(13) e(14) f(15)
op code is used as the value of instruction . And operand is address location where the instruction can meet.
In the 8085, the LDA instruction loads the accumulator from memory, while the STA instructionstores the accumulator to memory. LDA is a read, while STA is a write. LDA is opcode 3AH, while STA is opcode 32H.
i) Instruction code deals only with mnemonics and its corresponding opcode but data code refers to your data like 10h which is always of 8 bits or a particular address say 8080h which is of 16 bits. ii) Data is your input to the instruction but an opcode is native to your machine. iii) Data is user specific instruction while opcode is machine specific instruction iv) You can alter data code but you cannot modify an instruction opcode.
In the 8085, the LDA instruction loads the accumulator from memory, while the STA instruction stores the accumulator to memory. LDA is a read, while STA is a write. LDA is opcode 3AH, while STA is opcode 32H.
As far as the bus interface is concerned, there is no real difference between data and instructions. Except for the S0 pin, an opcode fetch will look the same as a memory read. There is one extra clock cycle following an opcode fetch, which is used by the CPU to decode and process the opcode, but the bus does not care because there is no sequence initiation with ALE.
Rhymes are one example of mnemonic devices. Other examples include music mnemonics, name mnemonics, word or expression mnemonics, and model mnemonics.
The microprocessor uses an opcode fetch cycle for every instruction because it has to know the opcode in order to execute it, and that is located in memory.
3 for opcode fetch, 1 for opcode decode, 3 for operand fetch, and 3 for opcode store, for a total of 10, not including wait states.