The highest priority in 8085 microprocessor system is
TRAP
8085 Interrupt Priorities Explained
The 8085 microprocessor handles interrupts, which are signals that temporarily halt the normal execution of a program to execute a special routine called an Interrupt Service Routine (ISR). Different interrupts have different priorities, determining which one gets processed first if multiple interrupts occur simultaneously.
Understanding 8085 Interrupt Types
The 8085 has several hardware interrupts. The main ones relevant to priority are:
- TRAP: This is a special type of interrupt.
- RST 7.5, RST 6.5, RST 5.5: These are restart interrupts, triggered by specific lines on the processor.
- INTR: This is a general-purpose maskable interrupt request line.
Interrupt Priority Levels in 8085
The 8085 microprocessor assigns priorities to these interrupts. The priority determines the order in which the processor responds to them. Generally, interrupts are prioritized based on their importance and whether they can be masked (disabled) by software.
- Non-Maskable Interrupts: These cannot be disabled by software using any instruction. They always get the highest priority.
- Maskable Interrupts: These can be enabled or disabled using specific instructions (like the EI and DI instructions).
In the 8085, the TRAP interrupt is the only non-maskable interrupt and therefore has the absolute highest priority. The other interrupts (RST 7.5, RST 6.5, RST 5.5, and INTR) are maskable.
Priority Order of 8085 Interrupts
If multiple interrupts occur at the same time, the 8085 processor handles them in a specific order based on their priority. The hierarchy is as follows, from highest priority to lowest:
| Interrupt Name | Type | Priority Level |
| TRAP | Non-Maskable | Highest |
| RST 7.5 | Maskable | High |
| RST 6.5 | Maskable | Medium |
| RST 5.5 | Maskable | Low |
| INTR | Maskable | Lowest |
Why TRAP is the Highest Priority
The TRAP interrupt is the highest priority interrupt because it is non-maskable. This means the processor cannot ignore or disable it through software commands. Additionally, TRAP is edge-triggered, meaning it responds only to a rising edge on its interrupt pin, making it suitable for urgent events like power failure detection.
Therefore, among the given options (RST 7.5, RST 6.5, INTR, TRAP), TRAP has the highest priority in the 8085 microprocessor system.
Important Questions from Program Interrupt
The register in the 8085A that is used to keep track of the memory address of the next op-code to be run in the program is the-
Match List-I with List-II
List I
List II
a.
Micro operation
i.
Specify micro operations
b.
Micro programmed control unit
ii.
Improve CPU utilization
c.
Interrupts
iii.
Control Memory
d.
Micro instruction
iv.
Elementary operation performed on data stored in registers
Choose the correct option from those given below:
Disabling an interrupt is known as ______.
The clock tick interrupts, which wakes up the processor from a halt state and allows the scheduler to pick other work to perform, is an example of _______.
Which is not true about an interrupt
