Important Features of bus lines created \ with PDP21/PDP22

• The PDP21 / PDP22 represents a tee unit.

  This means: If the bus node built in the PDP21 / PDP22 fails all remaining FieldBusPlugs are still connected with the bus master.

• All PDP21 / PDP22 connected to a bus line are supplied via the bus cable

  This means: To supply the FieldBusPlugs, a power supply unit is necessary that is situated best near the bus master.

  This is not a disadvantage, because without a bus master the data transmission is not possible.

  The advantage is that - under some circumstances - it is possible to supply the devices via the bus cable with 24 V DC saving local supply units.

  For more infomation see chapter “Supply” and the description of the devices.

• A bus line built with PDP21 / PDP22 is a real party line without branches or drops.

  This means: The max. baud rate of 12 Mbit/s is possible, provided that the termination on both ends is done correctly and the max. bus length is not exceeded.

• The contacts - pins and jacks - are gold plated.

  This means: Concerning the contacts, the PDP21 / PDP22 avoid that faults caused by loose or bad contacts.

• Only at the ends of the bus line, termination resistors are possible and necessary.

  This means: In the standard topology, as shown below, only at the ends of the line terminations are possible and necessary.

  At the Dsub9 connector, mounted on the bus master, the termination resistor set has to be switched ON and at the other end of the bus line the termination unit must be mounted.

Regarding the situation that 80 - 90% of the problems in conventional wired PROFIBUS® lines are caused by loose contacts or wrong termination, the FieldBus Plug system guarantees  a faultless data transmission line between the master and the slaves.