Digital Triggers

Digital Triggers handle inputs that are already digital but need conversion from voltage levels to 1 or 0 before being processed by the Input/Output unit.

Here, a pull-up or pull-down must be used so the input goes to a specific position when voltage or ground is not applied to the pin. There is no point in grounding a pin to indicate if the door has been opened if the pin is already at 0 V.

In fault tracing, one is often instructed to connect a jumper to a digital control module input with pull-up to ground. The diagnostic tool then changes the value between, for example, Off and On. This shows that the lead is whole.

Fig 1: Digital Triggers Voltage Circuit

Courtesy of SAAB-SCANIA OF AMERICA, INC.