Appendix B
Register-Level Programming — 82C53 Programmable Interval Timer (PCI-DIO-96, PXI-6508 Only)
PCI-DIO-96/PXI-6508/PCI-6503 User Manual
B-2
ni.com
82C53 Programmable Interval Timer
(PCI-DIO-96, PXI-6508 Only)
The PCI-DIO-96 and PXI-6508 contain an 82C53 programmable interval timer for use by
register-level programmers only. The 82C53 programmable interval timer can generate timed
interrupt requests to your computer. The 82C53 has three 16-bit counters, which can each be
used in one of six different modes. The PCI-DIO-96 and PXI-6508 can use two of the
counters to generate interrupt requests; the third counter is not used and is not accessible.
Refer to the
Programming Considerations for the 82C53
information.
Interrupt Control Circuitry
Two software-controlled registers determine which devices, if any, generate interrupts. Each
of the 82C55A devices has two interrupt lines, PC3 and PC0, connected to the interrupt
circuitry. On the PCI-DIO-96 and PXI-6508, the 82C53 device has two of its three counter
outputs connected to the interrupt circuitry. Any of these 10 signals can interrupt the computer
if the interrupt circuitry is enabled and the corresponding enable bit is set. Refer to the
Programming Considerations for the 82C53
section for more information. Normally, the
handshaking circuitry controls PC3 and PC0 of the 82C55A devices; however, you can
configure either of these two lines for input and then use them as external interrupts. An
interrupt occurs on the signal line low-to-high transition.
Refer to the
Programming Considerations for the 82C53
information concerning interrupts.