National Instruments 6508 PCI-DIO-96 - Manual (Page 66)

Chapter 6 Programming
PCI-DIO-96 User Manual 6-20 © National Instruments Corporation
Interrupt Handling
You must set the INTEN bit of Interrupt Control Register 2 to enable
interrupts from the PCI-DIO-96. Clear this bit first to disable unwanted
interrupts. After all sources of interrupts have been disabled or placed
in an inactive state, you can set INTEN. You must set INTEN before
you generate an interrupt for proper operation.
To interrupt the computer using one of the 82C55A devices, program
the selected 82C55A for the I/O mode desired. In mode 1, set either the
INTEA or the INTEB bit to enable interrupts from port A or port B,
respectively. In mode 2, set either INTE1 or INTE2 for interrupts on
output or input transfers, respectively. The INTE1 and INTE2 interrupt
outputs are cascaded into a single interrupt output for port A. After you
enable interrupts from the 82C55A, set the appropriate enable bit for the
selected 82C55A; for example, if you select both mode 2 interrupts for
PPI C, set CIRQ0 to interrupt the computer.
To interrupt the computer using one of the 82C53 counter outputs,
program the counters as described in the Interrupt Programming
Example section later in this chapter.
You can use external signals to interrupt the PCI-DIO-96 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. After you have
configured the selected 82C55A, you must set the corresponding
interrupt enable bit in Interrupt Control Register 1. If you are using
PC3, set xIRQ0; if you are using PC0, set xIRQ1, where x is the letter
corresponding to the PPI you want to generate interrupts (A–D). When
the external signal becomes logic high, an interrupt request occurs. To
disable the external interrupt, the interrupt service routine that you have
written should acknowledge the interrupt and write the interrupt clear
register.
Interrupt Programming Examples for the 82C55A
The following examples show the process required to enable interrupts
for several different operating modes. You must write and install the
interrupt service routine in order to process the interrupt and gain any
useful knowledge from it. You should clear all interrupt sources and
interrupt enable bits first to disable unwanted interrupts.