Specifications

Interrupt Controller (V40)
PROGRAMMABLE REGISTERS
The ICU is initialized with Interrupt Initialization Word 1 (IIW1)
through Interrupt Initialization Word 4 (IIW4). Once initialized, the
operation of the ICU is controlled with the Interrupt Mask Word
(IMKW), Interrupt Priority and Finish Word (IPFW), and Interrupt
Mode Word (IMDW). Three status words can also be read to
interrogate the operation of the ICU: the Interrupt Request (IRQ),
Interrupt In-Service (IISI), and Interrupt Poll (IPOL). Note that the
"word" reference does not mean the values are 16 bits; all
communication to the ICU is done through 8-bit data.
All initialization, operation, and status words are accessed through
two I/O addresses, as shown in Table 8-2. As might be expected, a
specific sequence of read and write operations is needed to pass
multiple bytes through a single I/O address. A complete description of
all the programmable words and how they are accessed is given on the
following pages.
Table 8-2
ICU Register Addressing.
Address Value Operation Page Number
Base + 0 IRQ, IIS, IPOL Read 8-16
Base + 0 IIW1 Write 8-8
Base + 0 IMDW, IPFW Write 8-13,8-15
Base + 1 IMKW Read/Write 8-12
Base + 1 IIW2, IIW3, IIW4 Write 8-8
8-7