What is the last mnemonic in ISR for an interrupt in 8085?

[rednewguy]

INTERRUPT-8085

what is the last mnemonic in the ISR for an interrupt in 8085. is it RET. how will the processor differentiate a return from a subroutine and an interrupt.

thanks

 

[dfullmer]

Re: INTERRUPT-8085

I asked my programmer about your question (old 8085 guy) and got this response. Hope this helps.

dfullmer

Since interrupt support is built into 8085, it handles
interrupts much like called subroutines.

Process:
Interrupt pin goes active (ex. 5.5)
8085 jumps to vector address (02CH for 5.5 int.)
Return address is automatically push onto stack so
return is easy and automatic.
Address of ISR in 02CH causes jump to ISR
Interrupts are now disabled
ISR performed
You must now manually re-enable interrupts and return
That is, last two op codes in ISR should be:
EI
RET
that's it.
I suppose if you wanted recursive or nested
interrupts, you could re-enable interrupts earlier in
the ISR.

 

[rednewguy]

Re: INTERRUPT-8085

Does the ISR saves only return address or both (return address and register values). should we have to explicitly store the register values? or the interrupt handler will itself do it?

 

[IanP]

Re: INTERRUPT-8085

Only the return address is saved ..

If you need to preserv the registers' values you need to do it in the very beginning of the ISR by using PUSH (and then POP) instruction ..
Of course, if a register is not used during interrupt you don't need to worry obout its value ..

Regards,
IanP