Interrupt Structure in 8085 microprocessor is one of the most important topic for programmer. programmer should have proper knowledge of it, at the time of writing any program. So before entering brief discussion, you may follow my early post “What are Interrupts in microprocessor 8085?” Now in this post, we will see Interrupt Structure in 8085 microprocessor.
As we know interrupt is the mechanism by which the processor transfer control from its current program execution to another program having higher priority checking. But some very important question will raise in our mind.
- Form where processor get those interrupt?
- How processor process those interrupt ?
Form where processor get those interrupt?
The interrupt signal may be given to the processor by any external peripheral device to different interrupts pin in 8085 microprocessor. That means interrupt can send by Keyboard, any input sensor etc.
How processor process those interrupt ?
After getting interrupt request from any device, it start the program or the routine that is executed upon interrupt is called interrupt service routine (ISR). After execution of ISR, the processor must return to the interrupted program. So to know the process step by step, we have to know the key features in the interrupt structure of any microprocessor. Which are as follows:
- Firstly, Number and types of interrupt signals are available.
- Secondly, The address of the memory where the ISR is located for a particular interrupt signal. This address basically called interrupt vector address (IVA).
- Thirdly, Masking and unmasking feature of the interrupt signals.
- Fourthly, Priority among the interrupts.
- Fifthly, Timing of the interrupt signals.
- Finally, Handling and storing of information about the interrupt program (status information).
When we discuss on Interrupt Structure in 8085 microprocessor then we should know that “What are the different type of interrupt present in 8085 microprocessor?“
Types of Interrupts:
We can classified interrupt depending upon some features. We can classified it based on their masking ability, IVA and source. Those are as follows:
Vectored and Non-Vectored Interrupts
- Vectored interrupts require the IVA should supplied by the external device that gives the interrupt signal. This technique is vectoring. And it can implemented in number of ways. The interrupts (TRAP, RST 7.5, RST 6.5 and RST 5.5) are also called vector interrupts. As each interrupt has fixed memory location (vector location) for the transfer of control from the normal execution of the routine. The vector locations of these interrupts shown in table.
- Non-vectored interrupts have fixed IVA for ISRs of different interrupt signals.
Maskable and Non-Maskable Interrupts
- Maskable interrupts are interrupts that can be blocked. Masking can done by software or hardware means. The RST 7.5, RST 6.5 and RST 5.5 are the maskable interrupts. The maskable means the prevention of any interrupt. Some times it may required to prevent one or more interrupts when a certain task is being carried out by the microprocessor. So the masking of these interrupts is done. The masking of any interrupt can carried out by an instruction known as SIM (Set Interrupt Mask).
- Non-maskable interrupts are interrupts that are always recognized; the corresponding ISRs are executed. TRAP is non-maskable interrupt.
Software and Hardware Interrupts
- Software interrupts are special instructions, after execution transfer the control to predefined ISR.The 8085 microprocessor has eight software interrupts namely RST 0, RST 1, RST 2, RST 3, RST 4, RST 5, RST 6 and RST 7.
These instructions are single byte instructions. When an interrupt occurs, a CALL instruction execute to a predetermined location of the memory. The effect of each restart instruction shown in table.
- Hardware interrupts are signals given to the processor, for recognition as an interrupt and execution of the corresponding ISR. Basically 8085 has five hardware interrupts INTR, RST 5.5, RST 6.5, RST 7.5 and TRAP.
If two or more of these interrupts are active at the same time then the 8085 takes them in order of priority level. The priority levels of these interrupts shown in table.
Let’s check how you learn Interrupt Structure in 8085 microprocessor with a simple quiz.
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Which interrupt has the highest priority?
What are level Triggering interrupts?
What are software interrupts?
What is SIM?
What is meant by Maskable interrupts?