User manual

Appendix D Register-Level Programming
PC-DIO-96/PnP User Manual D-36 © National Instruments Corporation
To interrupt the host computer using one of the 82C53 counter outputs,
program the counter(s) as described in the section, Interrupt
Programming Example for the 82C53, of this chapter.
External signals can be used to interrupt the PC-DIO-96/PnP when
port A or port B is in mode 0 and the low nibble of port C is configured
for input. If port A is in mode 0, use PC3 to generate an interrupt; if
port B is in mode 0, use PC0 to generate an interrupt. Once you have
configured the selected 82C55A, you must set the corresponding
interrupt enable bit in Interrupt Register 1. If you are using PC3, set
xIRQ0; if you are using PC0, set xIRQ1. When the external signal
becomes logic high, an interrupt request occurs. Although the host
computer’s interrupt-monitoring circuitry is triggered by the positive-
going edge of the interrupt signal, the signal must remain high until the
interrupt routine has been entered and interrupts have been masked out.
Make sure your external interrupt signal meets these qualifications. To
disable the external interrupt, clear the appropriate xIRQy bit or clear
the INTEN bit.