Digital Input
It is a command input with only two states (present / absent); the driver compares the input voltage with a threshold and interprets it as logic 1 or 0. On the KS250 the IN1–IN4 inputs take the clockwise start, reverse start, clockwise stop and reverse stop commands; on the PT500 there are four digital inputs labelled A, B, C and D.
A digital input suits any source giving a binary signal, such as a button, a relay contact, an RF receiver output or a PLC digital output. On the driver side the input usually reaches the microcontroller through a series resistor and a pull-up/pull-down resistor.
- Threshold: Above a certain voltage counts as logic 1, below it as logic 0. The region in between is undefined; half-made connections that leave the input there cause flickering behaviour.
- Unused input: An input connected to nothing behaves like an antenna and can be triggered by the switching noise on the motor cable. Terminate unused inputs as the schematic requires.
- Command logic: Separate start and stop inputs make it possible to build a latching behaviour driven by a momentary button; one pulse starts the motion, the other pulse stops it.
If the cable you connect to the input is long, run it on a route separate from the motor supply pair; digital inputs are more robust than analogue inputs but are not completely immune to noise.
The context in which this term is used: DC Motor Driver Selection Guide