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PNP and TTL/HTL Signal Handling in Digital Input Modules

Q.series digital input modules support both TTL and HTL logic levels and detect signal states based on the presence of a positive (PNP sourcing) voltage at the input terminal.

TTL & HTL logic levels

Logic level configuration per module type

  • A109: One global logic level setting applies to all digital inputs.

  • D101 / D104: The logic level can be configured per input group (per connection terminal).

  • D107: User-configurable logic levels with 256 steps:

    • Differential inputs: −20 VDC to +20 VDC

    • Single-ended inputs: 0 VDC to +26 VDC

TTL logic

  • Signal voltage (0 / LOW): < 0.8 VDC

  • Signal voltage (1 / HIGH): > 3.0 VDC

Note: Voltages between 0.8 V and 3.0 V are undefined and should be avoided.

HTL logic (EN 61131-2, Type 1)

  • Signal voltage (0 / LOW): −3 VDC to +5 VDC

  • Signal voltage (1 / HIGH): 11 VDC to 30 VDC

  • Specifications:

    • Maximum input voltage: 30 VDC

    • Maximum input current: 2 mA

    • Isolation voltage: 500 VDC

Note: Voltages between 5 V and 11 V are undefined and should be avoided for reliable switching.

Digital input signal wiring

In PNP (sourcing) operation, the sensor supplies a positive voltage to the digital input when active, which is interpreted as a HIGH signal. The sensor output is referenced to ground (0 V), so that the presence of voltage corresponds to ON and its absence to OFF. This approach is widely used due to its intuitive behaviour and improved fault detection, as a broken wire results in a defined OFF state.

Typical wiring:

Quick rule:

  • If the sensor outputs +V when ON → PNP → compatible

  • If the sensor switches to 0 V when ON → NPN → requires an interface

Configuration with GI.bench

  1. Double-click the module in the Project view to open the module settings window.

  2. Go to the Additional tab to access the logic level configuration parameters. The D101 and D104 modules provide separate logic level settings for the inputs on the first and second connector terminals.

  3. Click OK, then write the updated configuration to the controller.