NI-9361 Front End Control

The NI-9361 has 8 inputs that support both single-ended and differential modes. You can configure each of the input signals as the input to any of the 8 counters on the module. The following figure shows the circuitry of one of the digital inputs. Each digital input is similar.

Figure 7. Digital Input Circuitry

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I/O Protection

The voltage input level and the current input level of the digital signals are listed in the specifications of your device. The I/O protection circuitry protects the module in events such as overvoltage, overcurrent, and ESD. Refer to the NI-9361 Specifications for more information about the protection level supported.

Input Mode

You can configure the digital inputs to any of the following modes:
  • Single ended
  • Single ended with pull up
  • Differential
Note In single-ended and single-ended with pull-up modes, you must leave the corresponding DI- terminal open and connect the input signal to the corresponding DI+. You can set the programmable threshold voltage between 1 V to 4 V.

The NI-9361 provides a 5 V pull-up on each DI+ terminal which can be enabled individually. The 5 V pull up is about 1 kΩ, and is able to source up to about 5 mA of current to the sensor signal line connected to DI+. The pull up is useful for sensors with open-collector or open-drain outputs such as Hall Effect sensors. An open-collector device does not actively drive the signal high and relies on an external pull-up to perform this function.

In differential mode, there is no programmable threshold voltage. The 5 V pull up is disabled. The differential line signals are connected to the corresponding DI+ and DI- terminals.

Programmable Digital Filter

The NI-9361 has a digital filter on each of the digital input lines to filter unwanted glitches on the digital input signal.

You can configure the following filter properties for each of the input lines:
  • Enable or disable the digital filter.
  • Minimum pulse width of the input signal that passes through the filter.