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Instruction Sets, :check: Operation Code (Opcode)
Specifies the…
Instruction Sets
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Types of Operands
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:black_flag: Characters
- A common form of data is text or character strings.
- Textual data in character form cannot be easily stored or transmitted by data processing & communications system because they are designed for binary data.
:black_flag: Logical Data
- An n-bit unit consisting of n 1-bit items of data, each item having the value 0 or 1.
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Types of Operations
:forbidden: Data Transfer
- Location of the source and destination operands.
- The length of data to be transferred must be indicated.
- The mode of addressing for each operand must be specified.
:forbidden: Arithmetic
- provided for signed integer (fixed-point) numbers.
- also provided for floating-point and packed decimal numbers.
:forbidden: Logical
- Basic Logical Operations.
- Shift & Rotate Operations.
:forbidden: Conversion
- Instructions that change the format or operate on the format of the data.
:forbidden: Input / Output
- Variety of approaches taken :
- Isolated programmed I/O.
- Memory-mapped programmed I/O.
- DMA
- Use of an I/O processor.
:forbidden:System Control
- Instructions that can executed only while the processor is in a certain privileged area of memory.
:forbidden: Transfer of Control
- It is essential to be able to execute each instruction more than once.
- Virtually all programs involve some decision making.
- It helps if there are mechanisms for breaking the task up into smaller pieces that can be worked on one at a time.
:check: Operation Code (Opcode)
- Specifies the operation to be performed.
- The operation is specified by a binary code known as opcode.
:check: Source Operand Reference
- The operation may involve one or more source operands.
- Operands that are inputs for the operation.
:check: Result Operand Reference
- The operation may produce a result.
:check: Next Instruction Reference
- This tells the processor where to fetch the next instruction after the execution of this instruction is complete.
- All machine languages include numeric data types
- Numbers stored in a computer are limited :
- Limit to the magnitude of no. representable on a machine
- Three types of numerical data :
- Binary integer or binary fixed point
- Binary floating point
- Decimal
- Each decimal digit is represented by a 4-bit code with two digits stored per byte.
- To form no. 4-bit codes are strung together, usually in multiples of 8 bits.
