Specifications

Interrupt Controller (V40)
IRQ and IIS
The IRQ and IIS status words, shown in Figure 8-10 below, are
taken directly from the Interrupt Request register and Interrupt In-
Service register, respectively. The IRQ status word contains all
the interrupt levels requesting service. The IIS status word
contains all the interrupt levels currently being serviced. Bit 0 of
both status words corresponds to IRQ0, bit 1 corresponds to
IRQ1, and so on.
Register:IRQ
Address:Base + 0
Access:Read
76543210
IR7 IR6 IR5 IR4 IR3 IR2 IR1 IR0
Request Level/Status
0 No request
1 Request
Register:IIS
Address:Base + 0
Access:Read
76543210
IR7 IR6 IR5 IR4 IR3 IR2 IR1 IR0
In-Service Level/Status
0 Not in service
1 In service
Figure 8–10. Interrupt Status Registers IRQ and IIS.
IPOL
The two most common methods of servicing peripherals in most
applications are polling and interrupts. Although the ICU is
designed primarily for interrupt control, it can be used in a polled
system to increase the efficiency of servicing peripherals. The
efficiency is increased because the CPU can poll the ICU to
determine the status of several peripheral devices at one time.
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