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Instruction Classification

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8085 microprocessor instructions can be categorized into five different groups:
  • Data transfer operations group
  • Arithmetic operations group
  • Logical operations group
  • Branch operations group
  • Stack, Input/Output and Machine control operations group

Data transfer operations group: 

  • Data transfer instructions transfer data or copy data from source to destination. 
  • Source can be any data or contents of memory location or contents of any register. 
  • Destination can be register or memory location. 
  • These instructions do not affect the flag register.

Arithmetic operations group:
Arithmetic instructions perform:
  • addition 
  • subtraction 
  • increment
  • decrement operations.

Logical operations group:
The logical instructions perform:
  • logical operations like AND, OR, EX-OR
  • rotate operation
  • compare operation
  • complement operation

Branch operations group:
  • These instructions allow 8085 processor to change the sequence of the program under certain test conditions or unconditionally.
  • These instructions include branch instructions, subroutine call and return instructions, and restart instructions.

Stack, Input/Output and Machine control operations group:
  • These instructions control the stack operations, input/output operations and machine operations.
  • Stack instructions allow the transfer of data from stack memory to register pair and from register pair to stack memory.
  • Input/output instructions allow the transfer of 8-bit data to input/output port.
  • Machine instructions control the machine operations such as interrupt, halt or do nothing.

Important notations used in instructions:

M                         Memory location pointed by HL register pair
r                           8-bit register
Rp                       16-bit register pair
Rs                        Source register 
Rd                       Destination register
addr                    16-bit address
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