Branching instructions refer to the act of switching execution to a different instruction sequence as a result of executing a branch instruction.
The three types of branching instructions are:
- Jump (unconditional and conditional)
- Call (unconditional and conditional)
- Return (unconditional and conditional)
1. Jump Instructions – The jump instruction transfers the program sequence to the memory address given in the operand based on the specified flag. Jump instructions are 2 types: Unconditional Jump Instructions and Conditional Jump Instructions.
(a) Unconditional Jump Instructions: Transfers the program sequence to the described memory address.
| OPCODE | OPERAND | EXPLANATION | EXAMPLE |
|---|
| JMP | address | Jumps to the address | JMP 2050 |
(b) Conditional Jump Instructions: Transfers the program sequence to the described memory address only if the condition in satisfied.
| OPCODE | OPERAND | EXPLANATION | EXAMPLE |
|---|
| JC | address | Jumps to the address if carry flag is 1 | JC 2050 |
| JNC | address | Jumps to the address if carry flag is 0 | JNC 2050 |
| JZ | address | Jumps to the address if zero flag is 1 | JZ 2050 |
| JNZ | address | Jumps to the address if zero flag is 0 | JNZ 2050 |
| JPE | address | Jumps to the address if parity flag is 1 | JPE 2050 |
| JPO | address | Jumps to the address if parity flag is 0 | JPO 2050 |
| JM | address | Jumps to the address if sign flag is 1 | JM 2050 |
| JP | address | Jumps to the address if sign flag 0 | JP 2050 |
2. Call Instructions – The call instruction transfers the program sequence to the memory address given in the operand. Before transferring, the address of the next instruction after CALL is pushed onto the stack. Call instructions are 2 types: Unconditional Call Instructions and Conditional Call Instructions.
(a) Unconditional Call Instructions: It transfers the program sequence to the memory address given in the operand.
| OPCODE | OPERAND | EXPLANATION | EXAMPLE |
|---|
| CALL | address | Unconditionally calls | CALL 2050 |
(b) Conditional Call Instructions: Only if the condition is satisfied, the instructions executes.
| OPCODE | OPERAND | EXPLANATION | EXAMPLE |
|---|
| CC | address | Call if carry flag is 1 | CC 2050 |
| CNC | address | Call if carry flag is 0 | CNC 2050 |
| CZ | address | Calls if zero flag is 1 | CZ 2050 |
| CNZ | address | Calls if zero flag is 0 | CNZ 2050 |
| CPE | address | Calls if parity flag is 1 | CPE 2050 |
| CPO | address | Calls if parity flag is 0 | CPO 2050 |
| CM | address | Calls if sign flag is 1 | CM 2050 |
| CP | address | Calls if sign flag is 0 | CP 2050 |
3. Return Instructions – The return instruction transfers the program sequence from the subroutine to the calling program. Return instructions are 2 types: Unconditional Jump Instructions and Conditional Jump Instructions.
(a) Unconditional Return Instruction: The program sequence is transferred unconditionally from the subroutine to the calling program.
| OPCODE | OPERAND | EXPLANATION | EXAMPLE |
|---|
| RET | none | Return from the subroutine unconditionally | RET |
(b) Conditional Return Instruction: The program sequence is transferred unconditionally from the subroutine to the calling program only is the condition is satisfied.
| OPCODE | OPERAND | EXPLANATION | EXAMPLE |
|---|
| RC | none | Return from the subroutine if carry flag is 1 | RC |
| RNC | none | Return from the subroutine if carry flag is 0 | RNC |
| RZ | none | Return from the subroutine if zero flag is 1 | RZ |
| RNZ | none | Return from the subroutine if zero flag is 0 | RNZ |
| RPE | none | Return from the subroutine if parity flag is 1 | RPE |
| RPO | none | Return from the subroutine if parity flag is 0 | RPO |
| RM | none | Returns from the subroutine if sign flag is 1 | RM |
| RP | none | Returns from the subroutine if sign flag is 0 | RP |
Advantages:
Enables conditional execution: The branching instructions in the 8085 microprocessor allow for conditional execution of code, which can help optimize program flow and improve overall efficiency.
Simplifies programming: The branching instructions in the 8085 microprocessor simplify programming by providing a set of dedicated instructions for branching to different memory locations based on conditions.
Supports a wide range of operations: The branching instructions in the 8085 microprocessor support a wide range of operations, including conditional branching, unconditional branching, and subroutine calls.
Allows for loop execution: The branching instructions in the 8085 microprocessor can be used to implement loops by branching to a memory location that contains a loop instruction.
Disadvantages:
Limited branching range: The 8085 microprocessor has a limited branching range, which can restrict the amount of memory that can be accessed. This can be a disadvantage for applications that require a large number of branching instructions.
Limited number of condition codes: The 8085 microprocessor has a limited number of condition codes, which can restrict the types of conditions that can be tested.
Complex addressing modes: The addressing modes used in the branching instructions can be complex, which can make programming more difficult.
Limited instruction set: The 8085 microprocessor has a limited instruction set, which can limit the types of branching instructions that can be used. This can be a disadvantage for applications that require complex program flow.
Applications :
Looping: Branching instructions such as JMP, JZ, JNZ, JC, and JNC are used to implement loops in programs. This allows the program to repeat a set of instructions until a specific condition is met.
Decision-making: Conditional branching instructions are used to implement decision-making in programs. This allows the program to make decisions based on the current state of the microprocessor and branch to different parts of the program accordingly.
Subroutine calls: Call instructions, such as CALL and RET, are used to call subroutines in programs. This allows the program to reuse code and execute common tasks in a modular manner.
Interrupt handling: Branching instructions are used in interrupt handling to transfer control to an interrupt service routine. This involves branching to a different part of the program to handle the interrupt, and then returning to the main program after the interrupt is serviced.
Program flow control: Branching instructions are used to control the flow of programs by transferring control to different parts of the program based on specific conditions or events. This allows the program to execute specific tasks at specific times and in a specific order.