Rockwell Automation T8017 Trusted Peer to Peer Communications - Manual (Page 9)

Trusted
TM
Communication Software Package T8017
Issue 10 Mar 08 PD-T8017 9
1.1. Theory of Operation
Peer communications interaction is Master/Slave which provides deterministic behaviour. Each peer
communications subnet requires one Trusted
TM
system to act as the master for the subnet and up to
thirty-nine Trusted TM systems participating as slaves. If redundant masters are required so that a
subnet remains operational if the master peer goes offline, then another peer may be permanently set
as master. The two masters will arbitrate their control.
Peer communications is configured by defining peer subnet control boards and I/O boards within the
application program in the normal way. Each peer subnet control board defines the systems’ view of
one subnet of a network. Two control variables are provided on the peer subnet control board to define
the board as a master or slave and to give the application program control over the starting and
stopping of the peer to peer communications.
1.1.1. Communications Cycle
At start of the communications cycle, the peer master issues an enquiry command to the first slave. If
the master receives a response from the slave, it registers that slave as being active and then repeats
the process with the next slave. This sequence continues until all the slaves have been polled.
Enquiry 1
Master
Command
Slave
Response
Ack
Slave 1
Ack
Slave 2
Start Cycle
Enquiry 2 Enquiry 3 Enquiry 4
Ack Ack Ack
Enquiry 9
Slave 3 Slave 4 Slave 9
Figure 1 Peer Communications Start Cycle
The master then sends a transmit data command (token) to the first slave to instruct it to send its
output data to its configured peers. When the slave has completed this, it returns the token to the
master and the master repeats the process with the next slave. Once all the slaves have been polled,
the master transmits its output data. The transmit data cycle starts again with the first slave. The
master repeats this communications cycle continuously.
Figure 2 Peer Communications Transmit Data Cycle