1747-6.22, Backup Scanner User Manual

4-54 Operating Your SLC 500 Backup System
Publication 1747-6.22
Secondary Processor Remote Programming
Important: The programming device must be connected through the
DH+ network and must not bypass the relay in the
1747-BSN module (if the programs in both processor
are identical;e.g., if both DH+ mode addresses are the
same). If you were to connect the device directly to a
processor, it must be connected to the primary processor.
Therefore, if your system were to switch to the
secondary system, you must then move your device to
your new primary processor.
In the 1747 backup system, only the primary processor is connected
to the link. The secondary processor is not physically connected, but
it communicates with the secondary 1747-BSN module making this
processor think that it is on the DH+ network. This separate link
prevents Data Highway faults in the secondary processor.
The 1747-BSN backup module provides remote programming
capability for your secondary processor. This means that even with
the programming device directly connected to the primary processor,
the secondary SLC-500 processor memory can be programmed and/
or monitored.
The primary 1747-BSN module provides an access point for a
programming device to access the secondary processor. Using the
1747-BSN module, you can communicate from a programming
device across the backup modules to the secondary processor. You
must assign both the primary and the secondary processor the same
node address in the DH+ link. The 1747-BSN module reserves the
subsequent node address as an access-point address to the secondary
processor; that is, this address is accessed by a programming device
in order to program the secondary processor.
This means that if you set both processors node addresses to n, the
programming device can communicate with the secondary processor
with the node address n+1. Therefore, do not use node address n+1
for any other device on the DH+ network.
For example, a primary processor with node number 16 on DH+
network has the same address switch setting as the secondary
processor node.
However, in this situation, the terminal addressed to station 16
attaches to the primary processor and the terminal addressed to
station 17 attaches to the secondary processor.
Important: It is recommended to assign the same node address (n)
for both processors (primary and secondary) in a
redundant system. You must also reserve the next node
address (n+1) because this address is the access-point
address to the secondary processor.