Branch instructions in 8051 micrcocontroller

Explains different branch or jump instructions in 8051

1. Program flow instructions in 8051 (Conditional and Unconditional jump Instructions) A.Usha Rani Faculty, Department of Physics and Electronics St.Ann’s College for Women.

2. Program flow instructions These instructions are used to control the flow of execution of the program or to change the sequence of program execution. They are also called Branch instructions or Jump Instructions. Change the content of program counter to change the program execution order.

3. Unconditional Jumps Do not test any condition and Jump is taken always. Short Jump The program can jump to an instruction within 127 bytes in forward direction or 128 bytes in reverse direction. Also called relative jump because the address where the jump can be taken is relative to the address where the instruction is written. The instruction is SJMP rel (Jump to relative address rel )

4. Long Jump Used to jump to any location within entire program address space i.e., anywhere from 0000H to FFFFH. 3 byte instruction and is mostly used in large programs. The instruction is LJMP address Absolute Jump The entire program memory is divide into 32 pages each of 2K bytes each. AJMP can be used to jump within a page of 2K. The instruction is AJMP address

5. Conditional Jumps Test the condition before taking a jump. Jump is taken only if the condition given in the instruction is satisfied. Bit Jumps Check the status of a bit specified in the instruction before taking the jump. Jump is taken only if the condition specified in the instruction is satisfied. Used to monitor the status of a specified bit.

6. JC rel // Jump to relative address rel if C=1(Jump if Carry) JNC rel // Jump to relative address rel if C=0(Jump if No Carry) JB rel // Jump to relative address rel if bit =1(Jump if Bit) JNB rel // Jump to relative address rel if bit=0 (Jump if No Bit) JBC bit, rel // Jump to relative address rel if bit =1 and then clear bit (Jump if bit then clear)

7. Byte Jumps Check the byte of a data to make jump . JZ rel //Jump to relative address rel if A is 0(Jump if Zero) JNZ rel // Jump to relative address rel if A is not 0(Jump if Not Zero) CJNE A, direct,rel //Compare A with the contents of address direct and jump to relative address rel if they are not equal. If the contents of A are less than contents of address direct, set carry =1 otherwise clear carry(Compare and Jump if Not Equal)

8. CJNE A, # data,rel //Compare A with immediate value data and jump to relative address rel if they are not equal. If the contents of A are less than immediate value data, set carry =1 otherwise clear carry CJNE Rn , # data,rel //Compare Rn with the immediate value data and jump to relative address rel if they are not equal. If the contents of Rn are less than immediate value data, set carry =1 otherwise clear carry

9. CJNE @ Ri , # data,rel //Compare contents of address in Ri with immediate value data and jump to relative address rel if they are not equal. If the contents of address in Ri are less than immediate value data, set carry =1 otherwise clear carry DJNZ Rn,rel //decrement register Rn by 1 and jump to relative address rel if the contents of Rn are not zero after decrement operation.(Decrement and Jump if Not Zero)

10. DJNZ direct,rel //decrement contents of address direct by 1 and jump to relative address if the contents of address direct are not zero after decrement operation.

11. Thank you