#8 - PROFIBUS DP connector

PROFIBUS network connectors are extremely important for the performance of an industrial network. A practical recommendation is to use Siemens connectors as shown below.

• D-Sub (9-pin) male connector (Siemens references 6ES7972-0BB52-0XA0 or 6GK1500-0FC10):
  Pins:
  1 - Shield
  3 - Data Rx/Tx (B)
  4 - Repeater control signal
  5 - Ground
  6 - Power +5V
  8 - Data Rx/Tx (A)

• Termination resistance in red (as a general rule, put the network start and end devices ON, OFF the others. The exception is for connectors in Hubs, Repeaters where there must be the first connector in ON as well).

• The cables are grounded in the metallic part (clamp) shown above, which has a large contact area.
• Input (A1 and B1) and Output (A2 and B2) for the next daisy chain device. Pins A (negative - green) and B (positive - red) are responsible for the communication signals. Both work in a voltage range between LOW 1V and HIGH 4V.
  The voltage difference between pins B and A, that is B (positive) - A (negative), must be between 4V and 7V for good communication.
  If this voltage is higher than the maximum value indicated (7V), it is likely that you have a problem in the network, such as a lack of termination resistance or a cable break, which accentuates the signal reflections. At the other extreme, when this voltage is less than the recommended minimum (4V), it may indicate a short circuit or very long mains length.
• When there is only one wire to the connector, it MUST be in the IN position AND the terminator MUST be ON. When there are two connectors, then use both IN and OUT positions AND terminator OFF.
• Check the addresses of the Master and the Slaves.

A great tool for making good cable terminations is  Siemens' FastConnect .