User manual

29 Chapter 3
3.12 Interrupt Setting
When the interrupt occurs from MCX314/MCX314AS, the interrupt sig-
nal of MCX314/MCX314AS will be changed from high to low. Because
the PCI bus interrupt is high level sensitive, the PCI-1240/PCI-1240U
inverse the signal and latch the signal to adapt the PCI bus INTA. The
Fig- 3.17 shows the interrupt structure of the PCI-1240/PCI-1240U. We
suggest users who want to program their own interrupt service routine
(ISR) should follow the procedures:
Step 1: When interrupt occurs. (Hardware)
Step 2: Program will jump to ISR. (Software)
Step 3: In ISR program the first thing have to do is clear interrupt for pre-
venting hanging up the PCI bus.
Step 4: In ISR program the last thing have to do is read nRR3 of
MCX314/MCX314AS for accepting next interrupt occurs.
Figure 3.17: Circuit diagram of interrupt setting