Understanding Interrupts in the 8085 Microprocessor

The 8085 microprocessor is one of the earliest processors that laid the groundwork for modern computing. It has a complex but efficient mechanism of handling interrupts, which are signals that help manage the execution flow and respond to external events. Understanding these interrupts is crucial for effective programming and debugging.

Hardware Interrupts

Hardware interrupts in the 8085 microprocessor are generated by external devices and are used to signal the processor to perform specific tasks. These interrupts are necessary for real-time system management, such as responding to input from peripheral devices or managing external events in a timely manner.

Types of Hardware Interrupts

There are five types of hardware interrupts in the 8085 microprocessor, each with its own characteristics and priorities. Intr Interrupt Request: This is a general-purpose interrupt that can be used by any external device. RST7.5: A maskable interrupt with a higher priority than INTR. RST6.5: Another maskable interrupt with a priority between RST7.5 and RST5.5. RST5.5: A maskable interrupt with a lower priority than RST6.5 and RST7.5. TRAP: A non-maskable interrupt with the highest priority, which can be used for critical tasks and cannot be disabled by the processor.

Mechanisms of Hardware Interrupts

All five hardware interrupts have separate pins on the processor, which helps in avoiding the cost of a separate interrupt controller. Specifically: The INTR and TRAP interrupts are edge-triggered and latched, meaning they can be triggered by a single edge change and remembered until the interrupt is acknowledged. The RST 7.5, 6.5, and 5.5 interrupts are level-sensitive, meaning they trigger based on the level of the signal rather than the edge change.

Enabling and Disabling Interrupts

Interrupts are enabled by the EI (Enable Interrupts) instruction and disabled by the DI (Disable Interrupts) instruction. Additionally, the SIM (Set Interrupt Mask) and RIM (Read Interrupt Mask) instructions allow for more granular control over the maskable RST interrupts, allowing each to be individually masked. By default, all three RST interrupts are masked after a normal CPU reset.

Software Interrupts

Similar to hardware interrupts, software interrupts are also used to manage the flow of control within the program. However, software interrupts are generated by executing specific instructions in the code, such as the RST instructions, which are used to invoke specific interrupt vectors. The RST instructions can be used to call one of the eight interrupt vectors, RST0 to RST7, each of which corresponds to a specific memory address.

Each of these interrupts plays a crucial role in managing the flow of control in programs and responding to events in real time. By utilizing both hardware and software interrupts, the 8085 microprocessor provides a flexible and robust system for implementing tasks and handling unexpected events efficiently.

Summary

In the 8085 microprocessor, the following interrupts are available for managing the flow of control and handling events: Hardware Interrupts: INTR, RST7.5, RST6.5, RST5.5, TRAP Software Interrupts: RST0 to RST7 (generated by RST instructions) By understanding and leveraging these interrupts, developers can create more efficient and responsive applications for the 8085 microprocessor.