ORI Instruction Execution Timing
The execution time of a microprocessor instruction is measured in Machine Cycles (M-cycles) and Timing States (T-states).
- M-cycle: Represents a set of operations required to fetch and execute an instruction part.
- T-state: Represents one clock cycle, the basic time unit for microprocessor operations. One M-cycle consists of multiple T-states.
ORI Instruction Execution Breakdown
The $ORI$ (OR Immediate) instruction in processors like the 8085 typically involves the following steps:
- Opcode Fetch: The processor fetches the $ORI$ instruction's opcode from memory. This usually takes 1 M-cycle and 4 T-states.
- Operand Fetch & Execution: The processor fetches the immediate data byte from the next memory location and performs the logical OR operation between the data and the Accumulator's content. The result is stored back in the Accumulator. This takes 1 M-cycle and 3 T-states.
Total Execution Time
Combining the steps:
- Total M-cycles = 1 (Opcode Fetch) + 1 (Operand Fetch & Execute) = 2 M-cycles.
- Total T-states = 4 T-states (Opcode Fetch) + 3 T-states (Operand Fetch & Execute) = 7 T-states.
Therefore, the execution of the $ORI$ instruction requires 2 M-cycles and 7 T-states.
Important Questions from Instruction Set of 8085
The technique of assigning a memory address to each I/O device in the computer system is called -
In an 8085 microprocessor, the instruction CMP B has been executed while the contents of accumulator is less than that of register B. As a result, carry flag and zero flag will be respectively -
A fetch cycle is the
Determine the contents of accumulator if the instruction RAL is executed twice. Assume the contents of accumulator is AAH and CY = 0.
Calculate the time required to execute the entire instruction cycle if two machine codes, 0011 1110 and 0011 0010, are stored in memory locations 2000H and 2001H, respectively.
If the clock frequency is 2 MHz, the first machine code represents opcode to load data byte in the accumulator and the second code represents data to be loaded in the accumulator.
