The 8085 Non-Vectored Interrupt Process.

1.  The interrupt process should be enabled using the EI instruction.


2.  The 8085 checks for an interrupt during the execution of every instruction.


3.  If there is an interrupt, the microprocessor will complete the executing instruction, and start a RESTART sequence.


4.  The RESTART sequence resets the interrupt flip flop and activates the interrupt acknowledge signal (INTA).


5.  Upon receiving the INTA signal, the interrupting device is expected to return the op-code of one of the 8 RST instructions.

6.  When the microprocessor executes the RST instruction received from the device, it saves the address of the next instructionon the stack and jumps to the appropriate entry in the IVT.


7.  The IVT entry must redirect the microprocessor to the actual service routine.


8.  The service routine must include the instruction EI to re-enable the interrupt process.


9.  At the end of the service routine, the RET instruction returns the execution to where the program was interrupted.

•  The 8085 recognizes 8 RESTART instructions: RST0 -RST7.
            –  each of these would send the execution to a predetermined hard-wired memory location:

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