8085 Microprocessor Branch Instructions

YASH PAL,

8085 Microprocessor Branch Instructions – The branch instructions allow the microprocessor to change the sequence of a program, either unconditionally or under certain test conditions.

8085 Microprocessor Branch Instructions

Branch instructions are classified as:

  1. Unconditional Branch Instructions
  2. Conditional Branch Instructions

Unconditional Branch Instructions

JMP Address (16-bit)Jump unconditionally to the specified address and start execution from that address.
OperationPC ← Address
Length3 bytes
Addressing modeImmediate addressing mode
FlagsFlags are not affected.
CALL Address (16-bit)Jump unconditionally to the specified address after storing the address of the next instruction of the main program.
Operation[SP – 1] ← PCH
[SP – 1] ← PCL
SP ← SP – 2
PC ← address
Length3 bytes
Addressing modeImmediate addressing mode
FlagsFlags are not affected.
RETReturn from the subroutine unconditionally. The returning address is obtained from the stack and loaded into the program counter (PC).
OperationPCL ← [SP]
PCH ← [SP + 1]
SP ← SP + 2
Length1 bytes
Addressing modeIndirect addressing mode
FlagsFlags are not affected.

Conditional Branch Instructions

J condition address (16-bit)Jump to the specific address if the condition is true.
OperationIf the condition is true
PC ← address
Else
PC ← PC + 3
Length3 bytes
Addressing modeDirect addressing mode
FlagsFlags are checked but not affected.

The 8085 microprocessor has five flags. Out of these five, only four flags are available to the programmer to check the condition. The auxiliary carry (AC) flag is used internally and not available to the programmer to check the condition. Possible conditions for jump instruction are shown in the table below.

InstructionConditionComments
JC Address (16-bit)CY = 1Jump if carry
JNC Address (16-bit)CY = 0Jump if no carry
JZ Address (16-bit)Z = 1Jump if zero
JNZ Address (16-bit)Z = 0Jump if not zero
JP Address (16-bit)S = 0Jump if positive
JM Address (16-bit)S = 1Jump if minus
JPE Address (16-bit)P = 1Jump if even parity
JPO Address (16-bit)P = 0Jump if odd parity
Possible conditions for the JMP instruction
C condition address (16-bit)Call the subroutine at the specified address if the condition is true.
OperationIf the condition is true
[SP – 1] ← PCH
[SP – 1] ← PCL
PC ← Address
Else
PC ← PC + 3
Length3 bytes
Addressing modeImmediate addressing mode
FlagsFlags are checked but not affected.

Possible conditions for all instructions are shown in the table below.

InstructionConditionComments
CC Address (16-bit)CY = 1Call if carry
CNC Address (16-bit)CY = 0Call if no carry
CZ Address (16-bit)Z = 1Call if zero
CNZ Address (16-bit)Z = 0Call if not zero
CP Address (16-bit)S = 0Call if positive
CM Address (16-bit)S = 1Call if negative
CPE Address (16-bit)P = 1Call if even parity
CPO Address (16-bit)P = 0Call if odd parity
Possible conditions for CALL instruction
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