Configuring Counters (Scan Interface)

You can configure channels of some C Series digital input modules as counters. Counters measure digital signals. Counters are used commonly to count edges and for time measurements, such as measuring the frequency or period of a signal.

Configuring the Input Filter

You can add an input filter to all input channels of the module. A filter removes noise, glitches, and spikes on inputs by rejecting signals with periods shorter than the specified length. You can select one of the following options.

• Disabled—The hardware synchronizes the digital inputs using a 4 MHz timebase. Pulses longer than 250 ns are always detected. Pulses shorter than 250 ns may be rejected.
• 1 µs—Pulses shorter than 1 µs are rejected. Pulses between 1 µs and 2 µs are sometimes detected. Pulses longer than 2 µs are always detected.
• 16 µs—Pulses shorter than 16 µs are rejected. Pulses between 16 µs and 32 µs are sometimes detected. Pulses longer than 32 µs are always detected.
• 256 µs—Pulses shorter than 256 µs are rejected. Pulses between 256 µs and 512 µs are sometimes detected. Pulses longer than 512 µs are always detected.
• 4096 µs—Pulses shorter than 4096 µs are rejected. Pulses between 4096 µs and 8192 µs are sometimes detected. Pulses longer than 8192 µs are always detected.

Selecting the Measurement Mode

You can select one of four counter measurement modes for each counter channel: Count Edges, Period Measurement, Pulse-Width Measurement, or Frequency Measurement.