Where is request irq

Last modified on Skip to: content search login. Knowledge Base Toggle local menu Menus About the team. Knowledge Base Search. Log in. Options Help Chat with a consultant. Every device gets its chance, whether or not the device actually wants to communicate with the CPU. When the certain amount of time passes, the next device gets a chance to interact with the CPU. So, with polling each device in the system can interact with the CPU for a fixed amount of time, whether or not that device actually needs to communicate with the CPU, and whether or not there is enough time for device to send all messages to the CPU.

The second method of implementing communication between the CPU and other devices in the system is called interruption. Devices can use as much time as they need. Devices in our computer need to get the CPUs attention when they have work to do. Older systems used the polling method, which was not very efficient way.

Modern PCs use the interruption method. The first thing we have to know is that every expansion slot, every device or controller on the motherboard has one wire implemented which we call the interrupt wire.

Whenever current is applied to the interrupt wire, the connected device gets the CPUs attention. When the CPU detects the current on that pin, it will try to service the requesting device. The problem is that the CPU only has one physical interrupt connector, and the CPU typically has to service a lot of devices on the system.

All systems today have more than one device. The interrupt wire from each device is connected to the PIC chip. Device that needs attention applies current to its interrupt wire, but instead of going straight to the CPU, that current is picked up by the PIC chip. The CPU will then service the request from the device. For example, PCI devices can share interrupts, but other types of devices can not. That meant it had eight interrupts coming from the PIC chip, so we could have a maximum of 8 different devices attached to the bus.

Modern computers have 16 interrupts. Eight interrupts are added by cascading two PIC chips together. The second interrupt wire on the second PIC chip is connected to the second interrupt wire on the motherboard itself. Techopedia Terms. Connect with us. Sign up. Term of the Day.

Best of Techopedia weekly. News and Special Offers occasional. Interrupt Request IRQ. Techopedia Explains Interrupt Request IRQ Interrupts are commonly used to implement computing multitasking and effectively eliminate the requirement for the processor to sample poll the lines while waiting for external events.

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