Profibus Device Number Limit

Currently there is a limit of 64 devices that can be addressed on the Profibus DP card as when i try to add more it says the card if full.

Books On-Line states that 64 is the limit.

Can this limit be increased as there is 128 addresses on the card?

Is there a different type of card or anything new released that could increase this number? 

4 Replies

  • 64 is the limit of devices that can be communicated with a single Profibus card.
    128 is the address limit a single Profibus device can have and is set at the device and configured to match to allow communications.

    Device and address limits are not the same as it seems you are trying to make a correlation between.

    Add another Profibus card is the only option you have if you have more than 64 Profibus devices.

    You could use VIM and Profinet and get up to 128 devices but requires Profinet devices so I don't know if this is an option for you or not (Designing vs Already Installed).
  • In reply to Matt Stoner:

    Note, you can have two masters on the same Profibus segment. Each device binds to a single class 1 master. The Masters will pass a token so only one every talks at a time. The overall scan time of the segment will be that of all the devices. So adding 128 devices on one segment will result in longer scan time.

    If you are using Redundant DeltaV Profibus cards, you cannot have two of them on the same segment. That is because the Standby card occupies address 0, which cannot be changed. So although you can address two masters to be different addresses, there standby card would conflict. Having more than one master means using simplex cards.

    so as Matt points out, adding a second card is the easiest way to increase the number of devices you can integrate to the controller, and by using two segments, you get better performance on the segment, and you can use redundant cards. Note that the Profibus protocol supports multiple masters, Emerson does not recommend it, mainly because of the added latency introduced by the second master on the same segment. (you can also add a class 2 master to perform device maintenance tasks from a PC or even from AMS device Manager, for devices that have a EDD)

    If the current Profibus Segment was designed with more than 64 devices, the easiest thing is to break the segment at a reasonable location and bring that segment back to a second card. You can maintain the same device addressing in those devices. that is you don't have to readdress them to be from 1 to 64. The new Profibus master would be configured with those devices at their addresses.

    You can use Fiber media converters to keep the copper media segment distance to a minimum. The overall cable distance can impact the baud rate at which you operate the segment. Fiber extenders also avoid grounding issues between the DCS cabinet location and the device locations.

    Andre Dicaire