UNIT-1 (CHAPTER-2 TYPICAL INSTRUCTION SET OF 8085) MICROPROCESSOR AND PERIPHERALS

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UNIT-1 (CHAPTER-2 TYPICAL INSTRUCTION SET OF 8085) 

8085 Data-transfer Instructions

Data tranfer instructions are the instructions which transfers data in the microprocessor. They are also called copy instructions.

 Following is the table showing the list of Data-transfer instructions with their meanings.

 

Arithmetic instructions in 8085 microprocessor

Arithmetic Instructions are the instructions which perform basic arithmetic operations such as addition, subtraction and a few more. In 8085 microprocessor, the destination operand is generally the accumulator. In 8085 microprocessor, the destination operand is generally the accumulator.
Following is the table showing the list of arithmetic instructions:
 

Logical instructions in 8085 microprocessor

Logical instructions are the instructions which perform basic logical operations such as AND, OR, etc. In 8085 microprocessor, the destination operand is always the accumulator. Here logical operation works on a bitwise level.
Following is the table showing the list of logical instructions:
 

Branching instructions in 8085 microprocessor

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:

1. Jump (unconditional and conditional)
2. Call (unconditional and conditional)
3. 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.
 
(b) Conditional Jump Instructions: Transfers the program sequence to the described memory address only if the condition in satisfied.


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.
 
(b) Conditional Call Instructions: Only if the condition is satisfied, the instructions executes.
 
3. Return Instructions – The return instruction transfers the program sequence from the subroutine to the calling program. Jump 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.
 
(b) Conditional Return Instruction: The program sequence is transferred unconditionally from the subroutine to the calling program only is the condition is satisfied.

Machine Control Instructions in Microprocessor

These type of instructions control machine functions such as Halt, Interrupt, or do nothing. This type of instructions alters the different type of operations executed in the processor.
Following are the type of Machine control instructions:

 NOP (No operation) –

  

It is used when no operation is performed. No flags are affected during the execution of NOP. The instructon is used to fill in time delay or to delete and insert instructions while troubleshooting.

 HLT (Halt and enter wait state) –

  

 
The Microprocessor finishes executing the current instruction and halts any further execution. The contents of the registers are unaffected during the HLT state.

DI (Disable interrupts) –

  

Disable interrupt is used when the execution of a code sequence cannot be interrupted. For example, in critical time delays, this instruction is used at the beginning of the code and the interrupts are enabled at the end of the code. The 8085 TRAP cannot be disabled.

EI (Enable interrupts) –

  

After a system reset or the acknowledgement of an interrupt, the Interrupt Enable the flip-flop is reset, thus disabling the interrupts.

SIM (Set interrupt mask) – 

 

This SIM instruction is used to implementation of different interrupts of 8085 microprocessor like RST 7.5, 6.5 and 5.5 and also serial data output. It does not affect TRAP interrupt.

RIM (Reset interrupt mask) –

 

This is a multipurpose instruction used to read the status of 8085 interrupts 7.5, 6.5, 5.5 and to read serial data input bit.