Question

Explain Software Interrupt.

Answer 1

• The normal functioning of a microprocessor can be stopped by executing a special instruction, which is known as a software interrupt.
• The 8085 microprocessor supports eight user-defined software interrupts, numbered RST 0 to RST 7, where RST stands for restart.
• These interrupts are vectored interrupts, and when they occur, the control is automatically transferred to the corresponding memory location as indicated below.
  

  Interrupt	Mnemonics	Call Location (Hex)
  RST	0	0000
  RST	1	0008
  RST	2	0010
  RST	3	0018
  RST	4	0020
  RST	5	0028
  RST	6	0030
  RST	7	0038

• Software interrupts are not meant for handling asynchronous events. Instead, they are used to invoke software routines such as single-step execution and breakpoints.
• These interrupts are generated by executing interrupt instructions and may also occur due to arithmetic errors.
• After servicing these interrupts, the program counter is updated automatically. The microprocessor does not perform an interrupt acknowledge cycle and continues with the normal instruction cycle.
• Such interrupts cannot be disabled or masked and have higher priority than hardware interrupts.
• They are not used for interfacing external devices; therefore, they do not increase system throughput. Their main use is in program testing and debugging.