rtd DM5816, User Manual

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DM5816/DM6816 RTD Embedded Technologies, Inc.
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Fig. 1-1 – Module Layout Showing Factory-Configured Settings
P4, P16 — Interrupt Channel Select
(Factory Setting: Jumper installed on G; IRQ Disabled)
These header connectors, shown in Figure 1-2, lets you connect any one of four jumper selectable (P14)
interrupt sources to an interrupt channel, IRQ2 through IRQ15. XT channels 2 through 7 are jumpered on
P4 and AT channels 10 through 15 are jumpered on P16 (DM6816 only). In AT computers channels 2 and
9 are the same channel. To activate a channel, you must install a jumper vertically across the desired IRQ
channel’s pins. Only one channel on either P4 or P16 should be jumpered at any time. Figure 1-2a shows
the factory settings.
This module supports an interrupt sharing mode where the pins labeled G connect a 1 k-ohm pull-down
resistor to the output of a high-impedance tri-state driver which carries the interrupt request signal. This
pull-down resistor drives the interrupt request line low whenever interrupts are not active. Whenever an
interrupt request is made, the tri-state buffer is enabled, forcing the output high and generating an
interrupt. There are four IRQ circuits, one for the P14 jumper selectable interrupts and one each for the
incremental encoder channels. Their outputs are tied together through an "OR" gate, allowing all interrupt
sources to share the same IRQ channel. To determine which circuit has generated an interrupt on the
selected IRQ channel, read the status byte (I/O address location BA + 17) and check the status of bits 0
through 3, as described in Chapter 4. After the interrupt has been serviced, you must return the IRQ line
low, disabling the tri-state buffer and pulling the output low again. This is done by clearing the IRQ for
the source which generated the interrupt. You also can have two or more modules that share the same
IRQ channel. You can tell which module issued the interrupt request by monitoring each module’s IRQ
status bit(s). If you are not planning on sharing interrupts or if you are not sure that your CPU supports
interrupt sharing, it is best to disable this feature and use the interrupts in the normal mode. This will
insure compatibility with all CPUs. See chapter 4 for details on disabling the interrupt sharing circuit.