GE PACSystems RX7i, User Manual

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Chapter 7. Programming SRTP Channel Commands
GFK-2224Q January 2017 111
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Retrieve Detailed Channel Status
Up to 32
16
channels can be established by a PACSystems Ethernet Interface. Channels can be individually
monitored from the application program.
Note : The Embedded Ethernet interface in the CPE305 and CPE310 supports a maximum of 16
channels.
Note: The Embedded Ethernet Interface in the CPE330 and CPE400 supports up to 32 channels.
Channel Operations
Channel commands are based on the concept of periodic data transfers. The client (local) PLC uses a single
COMMREQ function to establish a channel (connection) to a server (remote) PLC and to request that specific
data be periodically transferred between the PLCs.
The Ethernet Interface automatically manages the establishment of communications and the periodic data
transfer. Parameters in the Command Block specify the frequency and direction of the transfer, and the
memory locations in the client and server to be used in the transfer.
Aborting and Re-tasking a Channel
There 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. This
aborts 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 Status
The Ethernet Interface status bits occupy a single block of memory, which is specified during configuration of
the Ethernet Interface. The status bits include Channel Status bits, which provide runtime status information for
each communication channel. Each channel has two status bits; the meaning of the channel status bits
depends 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 a
Channel Error bit.
For details of the status bits and their operation, refer to “Monitoring the Ethernet Interface Status Bits” in
Chapter 12, “Diagnostics.”
SRTP Channel Commands in a Redundant System
When configured for Redundant IP operation (see Chapter 1 for more information), only the active unit
establishes and maintains the SRTP Client connections used for the Channel commands. The backup unit does
not perform any SRTP Client operations. If SRTP Client operation is attempted, a COMMREQ error status is
returned to the local logic program. When the Ethernet interface changes from active to backup state, it takes
down 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 spare
SRTP Client connection for each connection using the Redundant IP address. That will prevent temporary
resource problems when establishing new SRTP Client connections to the new active unit while the previous
connections to the old active unit are being taken down.
16
The RX3i Embedded Ethernet interface supports a maximum of 16 channels.