XVME-212 Manual
August, 1989
When in the A position, the module cannot respond to interrupts because IACKIN* is not
monitored (IACKIN* is connected directly to IACKOUT* instead). When used in this
configuration, all poles of S2 should be closed to ensure that a programming bug does not
generate VMEbus interrupts.
When interrupts are going to be used, the jumpers must be in the B position.
2.4.7
Debounce Period Jumpers (J4-J 11)
When a mechanical switch closes, several contact bounces can be expected. Several
transitions or quickly changing input images can appear while the switch bounces. To
eliminate these bounces, circuitry is provided, which works as follows. When a change
is detected in an input, the change is not immediately reported to the scanner. Instead,
a timer, with time period, T, will start accumulating time. During this time, T, if the
input reverts to its original state (bounces), the timer is restarted and the change is not
reported. If the input does not bounce for the duration of time, T, the change will be
reported to the scanner at the end of time period T. This means that the input must
assume the new state and stay in the new state without bouncing for time, T, before the
change is reported to the scanner.
The value of time, T, is selectable via eight on-board jumpers. One and onlv one jumper
must be installed. This jumper defines the time, T, to be used by all 32 channels. The
following table shows the available selections.
Table 2-8. Debounce Period Jumpers
install
only
one
Jumper
T min
J l l
3.5 us
Jl0
7 us
J9 14 us
J8 28 us
J 7 112 us
J 5
448 us
J4 1.8 ms
J 6
14 ms
T max
4.5 us
9 us
18 us
36 us
144 us
576 us
2.3 ms
18 ms
Note
One (and only one) of the above jumpers must be
installed for proper module operation.
Note that the time associated with Jll is very short with respect to the opto isolator’s
response time. So selecting this time will essentially defeat the debounce circuitry for
users concerned about speed and not concerned about bounce.
2.5 INSTALLATION
The Xycom VMEbus modules are installed in a standard VMEbus backplane. Figure 2-3
2-9
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