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C-11
Counter/Timer Subsystem
The DAS-8 uses an Intel 8254 Programmable Interval Timer which
consists of 3 internal 16-bit counters, Counter 0, Counter 1, and Counter
2. The clock, gate, and output connections of Counters 0 and 1 are
undedicated and available on the DAS-8 external connector. Counter 2’s
gate and output connections are externally available also, but the clock
input is internally connected to either the PC bus clock or a 1MHz crystal
oscillator.
Logical Channels
The Logical Channels for the DriverLINX counter/timer subsystem
correspond to the following physical channels:
DriverLINX uses physical Counter 2 whenever the application requests
an internal clock for a data-acquisition task. The timing interval generated
by Counter 2 can vary from 2 to 65,535 clock tics. If a longer timing
interval is needed for an application, Logical Channels 3 or 4 can be
specified. Be sure to externally connect the appropriate lines as indicated
in the table. The availability of Logical Channels 3 and 4 is tested
whenever the analog input subsystem is initialized.
Table C-7. Corresponding Logical and Physical Channels
Logical
Channel
Physical Channel
0
Counter/timer 0
1
Counter/timer 1
2
Counter/timer 2
3
Counter/timers 2 and 1 (Connect CTR 2 OUT [6] to CTR 1 IN [4])
4
Counter/timers 2 and 0 (Connect CTR 2 OUT [6] to CTR 0 IN [2])
5
Counter/timers 0 and 1 (Connect CTR 0 OUT [3] to CTR 1 IN [4])
6
Pseudo-channel for external clock input at INTERRUPT IN [24]
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