Chapter 7. Programming SRTP Channel CommandsGFK-2224Q January 2017 111▪ Retrieve Detailed Channel StatusUp to 3216 channels can be established by a PACSystems Ethernet Interface. Channels can be individuallymonitored from the application program.Note: The Embedded Ethernet interface in the CPE305 and CPE310 supports a maximum of 16channels.Note: The Embedded Ethernet Interface in the CPE330 and CPE400 supports up to 32 channels.Channel OperationsChannel commands are based on the concept of periodic data transfers. The client (local) PLC uses a singleCOMMREQ function to establish a channel (connection) to a server (remote) PLC and to request that specificdata be periodically transferred between the PLCs.The Ethernet Interface automatically manages the establishment of communications and the periodic datatransfer. Parameters in the Command Block specify the frequency and direction of the transfer, and thememory locations in the client and server to be used in the transfer.Aborting and Re-tasking a ChannelThere are four ways a channel can be aborted:1. When the PLC CPU is stopped, all channels in use are aborted automatically.2. A channel (or all channels) can be aborted by issuing an Abort Channel command.3. A channel in use can be re-tasked by issuing an establish command for its channel number. Thisaborts the previous channel operation and then performs the new channel operation.4. A channel is also automatically aborted if a fatal error occurs.Monitoring the Channel StatusThe Ethernet Interface status bits occupy a single block of memory, which is specified during configuration ofthe Ethernet Interface. The status bits include Channel Status bits, which provide runtime status information foreach communication channel. Each channel has two status bits; the meaning of the channel status bitsdepends upon the type of communication performed on that channel.SRTP channels operation provides two Channels Status bits for each SRTP channel, a Data Transfer bit and aChannel Error bit.For details of the status bits and their operation, refer to “Monitoring the Ethernet Interface Status Bits” inChapter 12, “Diagnostics.”SRTP Channel Commands in a Redundant SystemWhen configured for Redundant IP operation (see Chapter 1 for more information), only the active unitestablishes and maintains the SRTP Client connections used for the Channel commands. The backup unit doesnot perform any SRTP Client operations. If SRTP Client operation is attempted, a COMMREQ error status isreturned to the local logic program. When the Ethernet interface changes from active to backup state, it takesdown all SRTP Client connections and their underlying TCP connections.Because it can take some time to take down a TCP connection, the Redundant system should reserve a spareSRTP Client connection for each connection using the Redundant IP address. That will prevent temporaryresource problems when establishing new SRTP Client connections to the new active unit while the previousconnections to the old active unit are being taken down.16 The RX3i Embedded Ethernet interface supports a maximum of 16 channels.
