Branch Group of Instructions in 8085 Microprocessor

Flashcards covering the 8085 Microprocessor's branch group of instructions, including program execution registers, conditional/unconditional jumps, calls, returns, and restart instructions.

Program Counter (PC)

A $16\text{-bit}$ register containing the memory address of the next instruction byte to be fetched; it is automatically incremented as bytes are fetched.

Instruction Register (IR)

An $8\text{-bit}$ special purpose register that receives the opcode portion of an instruction and is not accessible to the programmer.

Z register

An $8\text{-bit}$ register used to receive the LS byte portion of a $16\text{-bit}$ address in a $3\text{-byte}$ instruction; it is not accessible to the programmer.

W register

An $8\text{-bit}$ register used to receive the MS byte portion of a $16\text{-bit}$ address in an instruction; it is not accessible to the programmer.

JMP a16

An unconditional direct jump instruction ($3\text{ bytes}$) that loads the PC with the $16\text{-bit}$ address ($a16$) provided in the instruction.

PCHL

An unconditional indirect jump instruction ($1\text{ byte}$) that loads the PC with the contents of the HL register pair.

JNC a16

A conditional jump instruction that branches to address $a16$ only if the carry flag ($Cy$) value is $0$ (Jump if Not Carry).

JC a16

A conditional jump instruction that branches to address $a16$ only if the carry flag ($Cy$) value is $1$ (Jump if Carry).

JNZ a16

A conditional jump instruction that branches to address $a16$ only if the zero flag ($Z$) value is $0$ (Jump if Not Zero result).

JZ a16

A conditional jump instruction that branches to address $a16$ only if the zero flag ($Z$) value is $1$ (Jump if Zero result).

JPO a16

A conditional jump instruction that branches to address $a16$ only if the parity flag ($P$) value is $0$ (Jump if Parity Odd).

JPE a16

A conditional jump instruction that branches to address $a16$ only if the parity flag ($P$) value is $1$ (Jump if Parity Even).

JP a16

A conditional jump instruction that branches to address $a16$ only if the sign flag ($S$) value is $0$ (Jump if Positive).

JM a16

A conditional jump instruction that branches to address $a16$ only if the sign flag ($S$) value is $1$ (Jump if Minus).

Subroutine

A sequence of instructions (also called a subprogram or procedure) that can be called from several points in a program to avoid redundant rewriting.

CALL a16

A $3\text{-byte}$ instruction that saves the return address on the stack and then branches to the subroutine at address $a16$. ($\text{CALL a16} = \text{PUSH PC} + \text{JMP a16}$).

Return Address

The address of the next instruction after the CALL instruction; it is stored above the top of the stack during a CALL execution.

RET

A $1\text{-byte}$ instruction at the end of a subroutine that loads the PC with the return address popped from the top of the stack ($\text{RET} = \text{POP PC}$).

CNC a16

A conditional call instruction that branches to the subroutine at $a16$ only if the carry flag ($Cy$) value is $0$ (Call if Not Carry).

RNC

A conditional return instruction that effects a return to the main program only if the carry flag ($Cy$) value is $0$ (Return if Not Carry).

RST n

A group of eight single-byte restart instructions ($n = 0$ to $7$) that function as single-byte calls to the address calculated as $n \times 8$.

Restart Instructions

Instructions (like RST 1 on the ALS-SDA-85M kit) that generally transfer control to the monitor program, similar to restarting the processor kit.