ADLINK Technology NuDAQ PCI-7258 User Manual

ADLINK Technology NuDAQ PCI-7258 User Manual Manual pdf 30 page image

22 • Operation Theory4.2 Isolated Digital InputThe PCI-7258 contains 2 opto-isolated digital input channels. The circuitdiagram of the isolated input channel is shown below.Figure 8: Photo-CouplerThe digital input is routed through a photo-coupler (PC3H4), so that theconnections are not polarity sensitive whether using positive or negativevoltages. The PCI-7258 digital input has an inline 2.4kO resistor and theinput voltage can ranges from 0 to 24V.4.3 Interrupt ArchitecturePCI-7258 has a powerful dual interrupt routing scheme and the interruptsources are on the digital input channels 0 and 1. Using these interrupts willmake handling complicated digital information much easier and relief yourcomputer from the heavy burden of dealing with digital input data. Note thatdual interrupts does not mean the card occupies two IRQ levels. Theinterrupt will occur only when digital input level changes from 0 to 1. In otherwords, the interrupt condition occurs on the rising edge, triggered on the DIchannel. Be sure to clear the interrupt request after handling the ISR or thenext interrupt request will not be received normally. For more informationabout the interrupt operation, refer to section 5.6.DIGNDDI2.4 KO