8085 Microprocessor SIM and RIM Instructions: Interrupt Management

Understand how the SIM (Set Interrupt Mask) and RIM (Read Interrupt Mask) instructions manage interrupts in the Intel 8085 microprocessor. This guide details their functionality, explaining how they control interrupt enabling/disabling and provide a way to check the current interrupt status for efficient interrupt handling.

SIM and RIM Instructions in the 8085 Microprocessor

Interrupt Handling in the 8085 Microprocessor

The Intel 8085 is an 8-bit microprocessor that uses interrupts to handle external events or internal conditions asynchronously. Interrupts allow external devices or internal processes to signal the CPU to temporarily stop its current task and execute a specific routine (interrupt service routine) to handle the event. This ability is crucial for efficient system operation and responsiveness to external signals.

SIM (Set Interrupt Mask) Instruction

The SIM (Set Interrupt Mask) instruction in the 8085 microprocessor controls which interrupts are enabled or disabled. It doesn't take any operands. When executed, it copies the contents of the accumulator (A) into the interrupt mask register (IM). The IM register is an 8-bit register; each bit corresponds to a specific interrupt. A bit set to 1 enables the corresponding interrupt; a bit set to 0 disables it.

RIM (Read Interrupt Mask) Instruction

The RIM (Read Interrupt Mask) instruction reads the current state of the interrupt mask register (IM) and stores it in the accumulator. It allows the program to check which interrupts are currently enabled or disabled.

Using SIM and RIM Instructions

The SIM and RIM instructions work together to manage interrupts. SIM allows selective enabling/disabling of interrupts, while RIM provides a way to check the current interrupt status.

Example: Enabling RST 5.5 Interrupt

(The example from the original text showing how to enable the RST 5.5 interrupt while disabling others using SIM and RIM instructions is given here. The steps, including loading the accumulator, executing SIM, and executing RIM, are clearly shown.)

Comparing SIM and RIM Instructions

Conclusion

The SIM and RIM instructions provide fine-grained control over interrupt handling in the 8085 microprocessor. This is essential for efficient and reliable operation in systems that need to respond to interrupts.