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I am familiar with the RIM and SIM instructions that are available in the instruction set of microprocessor 8085. And thus I can enable RST 7.5 and RST 6.5 interrupts using SIM instruction and EI instruction. But how do I identify the interrupts? Suppose, if interrupt is likely to come on either of the RST 7.5 or RST 6.5, then how do I identify it?

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When you enable an interrupt on one of the 8085's RST5.5, RST6.5 or RST7.5 pins you will get behavior as follows:

RST5.5 is a maskable interrupt. When this interrupt is received the processor saves the contents of the PC register into stack and branches to 2Ch (hexadecimal) address.

RST6.5 is a maskable interrupt. When this interrupt is received the processor saves the contents of the PC register into stack and branches to 34h (hexadecimal) address.

RST7.5 is a maskable interrupt. When this interrupt is received the processor saves the contents of the PC register into stack and branches to 3Ch (hexadecimal) address.

So you sort out which one caused the interrupt based on where the code execution flow branches.

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  • \$\begingroup\$ Is it somehow possible to identify the interrupt using RIM instruction? \$\endgroup\$ – Rahul Kumar Singh Mar 7 '14 at 8:08
  • \$\begingroup\$ Yes, see this page. \$\endgroup\$ – Dave Tweed Mar 7 '14 at 14:35

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