ProSoft Technology 5205-104S-PDPS - Manual (Page 60)

4205/5205-TS-104S-PDPS ♦ ProLinx Standalone Protocol Implementation
IEC-60870-5-104 to PDPS Communication Module with Time Stamp
Page 60 of 128 ProSoft Technology, Inc.
July 12, 2007
2.2 Redundant Connections
The module supports redundancy by accepting two simultaneous client
connections. Only one connection can send/receive user data at a time, so the
module uses the STARTDT function to select to which client it will be exchanging
data. The module will send events and accept commands only to the client
connection that has sent the last STARTDT function.
The following diagram shows an example where the module sends five events to
two different clients. The module initially receives a STARTDT request from
Client 1 and therefore sends the following events to this client. After the third
event the Client 1 sends a STOPDT request and then Client 2 sends a
STARTDT request to the module. From that point on the module will send the
next events to Client 2 only.
Please note the following:
1 The STARTDT triggers the switch of the connection. Therefore, the STOPDT
request is not actually required from the current client to perform the switch
(although the previous diagram indicates the recommended communication
procedure)
2 The module will respond to any TESTFR requests received by both clients at
any time.
By selecting the E key (Display Program Status) the user can monitor the status
of both connections can be monitored. For the example below, the client
connected through Socket 1 is actively exchanging data to the module. This can
be confirmed since the START DT Active register has a value of YES (which
means that the last START DT received was through Socket 1).