There are two ways in which interrupt lines for hardware interrupts between the CPU and devices can be connected. A combination of both might be used within the same system.
A single interrupt request line might be shared between many devices.
- The line is active low, such that there is an interrupt when it transitions from
1to0- Denoted with a bar over the signal name
- A method is used to ensure one device cannot drive a logic 1 while another is driving a logic 0, which would cause a short circuit
- This provides flexibility, as more devices can be added to the shared line, and means we can use less pins
- Downside: More time has to be spent determining which of the devices on the line triggered the interrupt.
Alternatively, each device could have its own interrupt line.
- In this case, we know immediately known which device triggered the interrupt.
- More pins on the microcontroller are required.