CyberResearch PCIDIO 48H - Manual (Page 36)

Operation Theorem
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4.3.2 IRQ Level Setting
There is only one IRQ level requested by this card, although it is a dual
interrupt system. The motherboard circuits will transfer INTA# to one of the
PC IRQ levels. The IRQ level is set by the PCI plug and play BIOS and
saved in the PCI controller. Users can get the IRQ level setting by software
library.
Fig 4.3 Dual Interrupt System of PCIDIO 24H/48H/96H
(*) Note: This interrupt is not available in PCIDIO 24H
4.3.3 Note for Dual Interrupts
The PCI controller of PCIDIO 24H/48H/96H can receive two hardware IRQ
sources. However, a PCI controller can generate only one IRQ to PCI bus,
the two IRQ sources must be distinguished by the ISR of the application
software if the two IRQs are both used.
The application software can use the “_dioxxh_Get_Irq_Status” function to
distinguish which interrupt is inserted. After an ISR is completed, users must
check if another IRQ is also asserted, then clear current IRQ to allow the
next IRQ coming in.
The two IRQs are named as INT1 and INT2. In PCIDIO 24H/48H/96H, INT1
comes from P1C0, P1C3 or the event counter interrupt. INT2 comes from
P2C0, P2C3 or the timer interrupt. However in PCIDIO 24H, INT2 only comes
from timer interrupt. The sources of INT1 and INT2 is selectable by the
Interrupt Source Control (ISC) Register.
PCI
Controller
INTA#
IRQ
Flip-
Flops
INT1
INT2
Clear IRQ
INT1
MUX
P1C0
~P1C0 & P1C3
Event Counter
INT2
MUX
P2C0 (*)
~P2C0 & P2C3 (*)
Timer IRQ