Modern PROFIBUS connectors have one cable input marked "ingoing" and one cable output marked "outgoing". This differentiation is very important, because the plug will switch off the cable output if the termination resistor is switched on. Connectors like this are very useful for testing and commissioning a network. If such a connector in the middle of a segment has a termination switched on, the part of the segment connected to the output will be isolated while the remaining network will still be correctly terminated. For this reason, the first and last connectors must only use an "ingoing" cable input.
Connectors often have a built-in switch that interrupts the bus if the bus termination is switched on. |
At the end and beginning of the bus, the cable must only be inserted at the input. |
In the middle of a bus segment, both cables are connected. The cable input leads to the master. |
If a connector does not have a breaker, it is not obvious when additional bus terminations are switched on. The signal will be damped by the additional bus termination and sporadic transmission faults may arise.
When interrupting connectors are used, switching on an additional bus termination will inevitably lead to interruption of the bus and therefore to a static and easily identifiable error.
D-type connector
Connector with bus termination switched on
Connector with bus termination switched on and breaker