Peer-to-Peer Communication - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 13.1

Controller Tool Help

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Controller Configuration Tool
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User Guide
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The peer-to-peer configuration provides communication directly between two devices on a trunk (for example, communication between two Field Controllers). This setup allows a device to read values from another device or write values to it using Network Input Modules or Network Output Modules . To read a value from another device, set up peer-to-peer communication using a Network Input. The recommended method for peer-to-peer communication is reading values from other devices (as opposed to writing values to devices). To write a value to another device, set up peer-to-peer communication using a Network Output (for example, to send a value to a third-party device). Configure the Peer Reference attribute in the Network Input or Output to enable or disable the communication.

Peer-to-Peer Communication Devices:

Note: N2 devices do not support peer-to-peer communication.
  • Johnson Controls Devices: Peer-to-peer communication occurs between two Johnson Controls devices (for example, two Field Controllers). The updates for network inputs are done based on change of value (COV). Network outputs write to the output reference when its value changes.

  • Third-Party MS/TP Device: Peer-to-peer communication occurs between a Johnson Controls device and a third-party MS/TP device (for example, a Field Controller and a TEC). In this case, the reference is a poll with a poll rate of 30 seconds, which cannot be changed. The network output writes to its output reference only when a value changes.

Guidelines for Peer-to-Peer Communication:

  • You should not exceed 15 network outputs with peer references per device.

  • We recommend a limit of 50 network input references to a single device. That is, do not define a single device as the source of peer-to-peer data to more than 50 other devices. For example, if you have 10 network input references on three devices, and 5 network input references on four devices, you have 50 total references (3 x 10 + 5 x 4).

    Note: Peer-to-peer communication requires processor time on both devices and bandwidth on the MS/TP communication bus.
  • We recommend that you do not exceed a token loop time of 2 seconds (2,000 milliseconds) under normal operating conditions. Keep in mind that the more peer-to-peer references you define, the longer it takes for the token to pass around the loop.

  • The preferred method of peer-to-peer communication for Field Controllers is to use Network Inputs to reference a source. Using a Network Input with a referenced source allows the reliability of the reference to be used in logic (for example, for referencing the OA-T analog input).

  • If you use Network Outputs to send a value to a peer controller, make sure that the destination is only sent a value from a single source (that is, avoid using fan-in references from multiple Network Outputs).

  • You must configure peer-to-peer communication in the Configuration mode.

    Note: If you change peer-to-peer references in Commissioning mode, the communication works until the controller loses power. When the controller resets, the peer-to-peer reference changes are lost. To resolve this problem, make the necessary peer-to-peer communication changes in the Configuration mode, then transfer the application to the controller.

Examples of Peer-to-Peer Communication:

  • Many applications provide a Network Input for Outdoor Air Temperature when a physical sensor is not installed. You can use peer-to-peer communication to reference the OA-T analog input on a different controller on the same MS/TP Field Bus.

  • You can configure the Unit Enable input of cooling only VAV boxes to reference the Supply Fan Status BI (SF-S) of the Air Handling Unit that serves them.

  • You may no longer need to configure Global Data Sharing in the Supervisory Controller. For example, in previous releases you had to define an Outdoor Air Temperature object in the Supervisory Controller and use Global Data Sharing to write the Outdoor Air Temperature to the necessary Field Controllers. Using peer-to-peer communication, reference the OA-T analog inputs on the Field Controllers located on the same MS/TP Field Bus.

For more information, see the following sections: