Measurement Computing DaqBoard 3000USB Series - Manual (Page 42)

1-16 Device Overviews 988093 DaqBoard/3000USB Series User’s Manual
Counter Inputs
Four 32-bit counters are built into each DaqBoard/3000USB Series board. Each of the four counters
accepts frequency inputs up to 20 MHz. The high-speed counter channels can be configured on a per-
channel basis. Possible configurations include the following modes:
o Counter
o Period
o Pulse width
o Time between edges
o Multi-axis quadrature encoder
Reference Note:
For detailed information regarding the various counter modes refer to Chapter 5,
Counter Input Configuration Modes.
The counters can concurrently monitor time periods, frequencies, pulses, and other event driven
incremental occurrences directly from encoders, pulse-generators, limit switches, proximity switches, and
magnetic pick-ups.
As with all other inputs to the boards, the counter inputs can be read asynchronously under program
control, or synchronously as part of an analog and digital scan group based on a programmable internal
timer or an external clock source.
The boards support quadrature encoders with up to 2 billion pulses per revolution, 20 MHz input
frequencies, and x1, x2, x4 count modes. With only A-phase and B-phase signals, 2 channels are
supported. With A-phase, B-phase, and Z-index signals, 1 channel is supported.
Each input can be debounced from 500 ns to 25.5 ms (total of 16 selections) to eliminate extraneous noise
or switch induced transients. Encoder input signals must be within -5V to +10V and the switching
threshold is TTL (1.3V).
Timer Outputs
Two 16-bit timer outputs are built into every 3000 series board. Each timer is capable of generating a
different square wave with a programmable frequency in the range of 16 Hz to 1 MHz.
Example 6: Timer Outputs
Timer outputs are programmable square waves. The period of the square wave can be as short as 1us or as
along as 65536 us. See the table below for some examples.
Divisor* Timer Output Frequency Related Equations
0 1 MHz
99 10 kHz
999 1 kHz
4999 200 Hz
9999 100 Hz
65535 Turns Timer OFF *
F = 1 MHz / (Divisor + 1)
Divisor = (1 MHz / F) - 1
* The divisor range is 0 to 65535. For Setpoint Operation 65535 turns the timer off.
In Asynchronous Write, 65535 results in a timer output frequency of 15.259 Hz.
There are 2 timer outputs that can generate different square waves. The timer outputs can be updated
asynchronously at any time. Both timer outputs can also be updated during an acquisition as the result of
setpoints applied to analog or digital inputs. See the section on pattern detection setpoints for more
information and examples.