Change-of-State Interrupts
At Power-up or Reset, a latch disables all IRQ sources on the card. In order to properly disable/enable
interrupts, you must program the Change-Of-State Interrupt Enable Register first. To program this Change-
of-State-Interrupt-Enable Register, write to it at Base B. Data bits D0 through D5 control ports A,
B, and C of the 8255 PPIs as shown in Table 4. Any access of Base+B will enable the non-COS IRQ
associated with
port C bit 3.
Bit
Port Controlled
D0
Group 0, Port A
D1
Group 0, Port B
D2
Group 0, Port C
D3
Group 1, Port A
D4
Group 1, Port B
D5
Group 1, Port C
Table 6-3:
Change-of-state-interrupt-enable Register
Writing a "one" disables the port; writing a "zero" enables it. When IRQs occur the interrupt state is latched.
To clear the latch, write anything to Base F.
Manual PCI-DIO-48(S)
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