Configuring a Peer-to-Peer Subnet

When configuring the Peer-to-Peer subnet, define these settings:
Setting
Description
Subnet ID
The number identifying the Ethernet network for the controller. Possible values are 1 to 8.
Network Interface
The processor slice that the peer network is physically connected to. Possible values are Processor Slice A, Processor Slice B, Processor Slice C, or No Connection.
Response Timeout (ms)
The amount of time for a peer to acknowledge reception of a data packet, in milliseconds. Possible values range from 0 to 10000 ms. The default value is 0 ms.
Set the value above 0 to avoid network packet sequence errors, which occur when the propagation delay between two nodes exceeds 1 ms. The value must be greater than the propagation delay (measurable by using the
ping
 command).
Set to 0 when no acknowledgment is required. For example, no acknowledgment is required if the entire Peer-to-Peer network is on a local Ethernet network and contains no routers or gateways.
The
Response Timeout
 acts as a watchdog trip for a lost packet and should be the shortest value for the timeout settings.
NOTE: To provide some tolerance to message loss, a slave is only declared inactive (FALSE) after the occurrence of two consecutive response timeouts.
Refresh Timeout (ms)
The maximum amount of time, in milliseconds, the peer controller waits during a cycle for the master to signal to the peer to transmit the output data. Possible values range from 0 to 10000 ms. The default value is 2000 ms.
The Refresh Timeout value is calculated by multiplying the
Slave Transmit Timeout
 value with the number of peers lost on a worst case network break.
When the Refresh Timeout expires, the peer discards any data to transmit and considers the network inoperable. The network must be reactivated by the master.
If the network is broken, the
Slave Transmit Timeout
 trips, minimizing the loss of data transfer.
Slave Transmit Timeout (ms)
The amount of time, in milliseconds, that a subnet master controller waits for a slave to complete transmission of the output data and return control of the network before declaring the slave absent. The
Slave Transmit Timeout
 is only used by the master of a subnet. Possible values range from 1 to 10000 ms (a minimum of 64 ms is recommended). The default value is 500 ms.
The Slave Transmit Timeout acts as a watchdog for a lost slave, allowing enough time for the slave to send all the outputs even if the slave is waiting for lost packets from the
Response Timeout
 setting.
A slave is only declared inactive (FALSE) after the occurrence of two consecutive timeouts. The slave remains inoperable until reactivated by the subnet master.
To calculate the Slave Transmit Timeout value, do the following:
  • (
    Response Timeout
     of the slave) x (Maximum number of output data boards in any controller) + 16 ms
  • When the
    Response Timeout
     value of the slave is 0 ms, use 2 ms in the previous calculation.
Enable Controller
The wired variable starts or stops the peer communications for the controller. Possible values are TRUE or FALSE.
  • TRUE - Enable Peer-to-Peer communications
  • FALSE - Disable Peer-to-Peer communications
Master/Slave
Sets if the controller is a master or slave. Possible values are TRUE or FALSE.
  • TRUE - The controller acts as a master
  • FALSE - The controller acts as a slave
Set at least one master to enable Peer-to-Peer communication.
IMPORTANT: To use Peer-to-Peer communications on both ports of a processor, configure IP addresses with different subnets.
To configure a peer-to-peer subnet
  1. In the Communication View, right-click the required Peer-to-Peer network instance, and then click
    Add Subnet
    .
    The
    Subnet Configuration
     dialog box displays.
  2. In the
    Subnet Configuration
     dialog box, set the Subnet ID and then click
    OK
    .
  3. In the Communication View, double-click the subnet instance.
    The Communication property page displays.
  4. In the property page, enter the required values for the following properties:
    • Network Interface
    • Response Timeout
    • Refresh Timeout
    • Slave Transmit Timeout
  5. Click cmv_wv to wire variables for the following parameters:
    • Enable Controller
    • Master/Slave
  6. (optional) To delete a peer-to-peer subnet, in the Communication View, right-click the subnet instance to remove, and then click
    Delete
    .
    TIP: Networks must always have at least one subnet; the last remaining subnet under a network cannot be removed.
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