Precautions For Duplex Systems - Omron CS1W-CLK12-V1 Operation Manual

Precautions for Duplex Systems

8-4 Precautions for Duplex Systems
176
• If an error occurs in an active Controller Link Unit and there is an active/
standby switchover, or if an active Controller Link Unit is replaced online,
because the relevant node will temporarily leave and then re-enter the
network, communications operations (both message communications and
data links) will be temporarily stopped. At this time, the Data Link Partici-
pation Flag for the relevant node will turn OFF, and the Communications
Error Flag will turn ON. After the switchover, communications will resume
and the status will return to normal (the Data Link Participation Flag turns
ON and the Communications Error Flag turns OFF). For this reason, per-
form the following processing in systems where there are duplex nodes in
the network.
• When using message communications, set the number of retries for
the SEND, RECV, and CMND instructions (i.e., set the number of re-
tries in the control data to a value other than 0), and be sure to perform
resend processing for instructions.
• When using data links, while communications operations are stopped,
data will not be sent or received for the relevant node. (Data sent or
received, however, via data link immediately before communications
stopped will be saved.) Therefore, if necessary for the application, in-
clude processing to control whether data received via data link after
communications resumes (i.e., when the Data Link Participation Flag
changes from OFF to ON and the Communications Error Flag chang-
es from ON to OFF) is enabled or not. (Include processing in the ladder
programs for the CPU Units at the relevant node and the data link des-
tination node).
A theoretical value for the time required for communications to resume can
be obtained using an equation. (Refer to 8-5 Switching Time for Duplex
Units.)
• Units can only be used in duplex operation if duplex-compatible Controller
Link Units (CS1W-CLK12-V1 and CS1W-CLK52-V1) are mounted to the
CS1D PLC. The CS1W-CLK12 or CS1W-CLK52 cannot be used in
duplex operation.
• Units can be used in duplex operation in either CS1D Duplex Systems or
CS1D Simplex Systems.
• When using Units in duplex operation, use Controller Link in token-ring
mode. Token-ring mode's transmission path duplication and the CS1D
System's duplex function for Communications Units allow the creation of a
highly reliable network. If used in token-bus mode, the network will be
temporarily split into two networks when Controller Link Units are
replaced online because the transmission path is not duplicated.
• Controller Link Units using up to 4 different unit numbers can be mounted
on a single CS1D PLC (including Expansion Racks). Only 3 unit numbers
(i.e., 3 pairs of Units), however, can be used in duplex operation. The
maximum numbers of mountable Units for different combinations of
duplex/non-duplex operation, where all 4 unit numbers are used, are
given in the following table.
Used in duplex Not used in
operation duplex
operation
3 pairs of Units 1 Unit
2 pairs of Units 2 Units
Maximum number of mountable Units
3 active Units + 3 standby Units + 1 Unit =
7 Units in total
2 active Units + 2 standby Units + 2 Units =
6 Units in total
Section 8-4