In computer architecture, micro-instructions are low-level instructions used to implement higher-level machine instructions. The format of a micro-instruction varies depending on the specific architecture, but typically includes several fields that specify the control signals necessary to execute the instruction.
The basic format of a micro-instruction consists of the following fields:
- Control Field
- Address Field
- Conditional Field
- Next Address Field
1. Control Field:
The control field specifies the control signals necessary to execute the instruction, such as the source and destination registers, the operation to be performed, and the next address to be executed.
2. Address Field:
The address field specifies the memory address of the micro-instruction. This field is used by the control unit to fetch the next micro-instruction from memory.
3. Conditional Field:
The conditional field specifies whether the current instruction should be executed based on a specific condition, such as a comparison between two registers or a flag bit in a status register.
4. Next Address Field:
The next address field specifies the memory address of the next micro-instruction to be executed. This field is used by the control unit to determine the next micro-instruction to fetch from memory.
The format of micro-instructions can vary depending on the architecture and the complexity of the instructions being executed. Some architectures may include additional fields, such as a field for specifying the number of cycles required to execute the instruction, or a field for specifying the type of memory access required.
Micro-instructions are typically stored in a control memory or control store, which is a type of memory that contains the microcode necessary to execute the machine instructions. During execution, the control unit fetches the appropriate micro-instruction from the control memory and executes it, using the control signals specified in the control field to perform the necessary operations.