To work with 8085 microprocessor, we should know Interrupt Sources and Vector Addresses in 8085 microprocessor. In 8085 microprocessor, it has two sources by using those sources we can interrupt the 8085 microprocessor. Those two interrupt sources are 1) Software interrupt and 2) hardware interrupt. In bellow we will see what is software and hardware interrupt.
Software interrupt is special kind of interrupt which programmer can use as an instruction. If we look on instruction set of 8085 microprocessor includes eight software interrupt instructions called Restart (RST) instructions. These are one byte instructions that make the processor execute a subroutine at predefined locations. That means when programmer use those instruction in between program, at the time of execution of the program it stop execution current program and jump to the subroutine of that interrupt instruction. Instructions and their vector addresses are given in Table.
The software interrupts can be treated as CALL instructions with default call locations. Now question is if we use more than one software instruction inside any program then which work perform first. The concept of priority does not apply to software interrupts as they are inserted into the program as instructions by the programmer and executed by the processor when the respective program lines are read.
Hardware Interrupts and Priorities:
In 8085 microprocessor have five hardware interrupts. Those are INTR, RST 5.5, RST 6.5, RST 7.5 and TRAP. Now for unlike software interrupt hardware interrupt has own priority level. Their IVA and priorities are given in billow Table.