Safety Considerations Guide, Tricon v9.0 - Tuv-fs.com

Examples of Peer-to-Peer Applications 73Controlled Use of TR_USEND/TR_URCV Function BlocksThe networks in this example show how to use TR_USEND/TR_URCV functionblocks correctly, in a controlled way, so that a limited amount of important data canbe transferred between two applications when new data is ready to be sent.This example uses the following project elements:• PEER_EX3_SEND_FBD (for sending Node #2)• PEER_EX3_RCV_FBD (for receiving Node #3)Using TR_USEND/TR_URCV Function Blocks for Safety-Critical DataThis example shows how to use TR_USEND/TR_URCV function blocks fortransferring a limited amount of safety-critical data between the two applicationsas fast as possible. It also shows how to measure the actual maximum time fortransferring data from the sending node to the receiving node. Because this issafety-critical data, each controller must have two NCMs and two peer-to-peernetworks connected.Sending Node #1 Parameters:• Scan time (SS) = 150 milliseconds• Number of aliased variables in bytes = 2000• Time to transfer alias data over the communication bus in milliseconds (TS)= (2000/20000) * 1000 = 100 milliseconds• The sending controller has only one TR_USEND function block in theapplication, meeting the requirement to have five or fewer TR_USENDfunction blocks. The sendflag is on in the TR_USEND function block sothat, as soon as the last TR_USEND is acknowledged by the receivingcontroller, the sending controller initiates another TR_USENDReceiving Node #3 Parameters:• Scan time (SR) = 200 milliseconds• Number of aliased variables in bytes = 5000• Time to transfer aliased data over the communication bus in milliseconds(TR) = (5000/20000) * 1000 = 250 milliseconds• Process tolerance time = 4 secondsAppendix APeer-to-Peer Communication