Programming the Local Host
Chapter 5
55
Memory Access Rungs
Memory access rungs define blocks of data table words which can be
accessed with protected write commands from the remote node you
specify. Protected write commands received from the specified remote
node may access only those blocks of local data table words listed in
memory access rungs. However, with no memory access rungs, the local
node will accept protected write commands from any remote node to
access any part of the data table.
WARNING: Unprotected write commands override any
memory access rungs. Use them with discretion because writes
to unauthorized data table areas can result in damage to
equipment and personnel. Don’t forget that to allow access to
data table write commands from any remote node, you must set
the accept-writes-to-data-table switch to ON (Chapter 4).
A memory access rung is composed of one or more memory access
branches, as shown in Figure 5.3. In the memory access branch format, a
branch start precedes a group of elements. The EXAMINE-ON and GET
elements in the memory access branch specify the following:
The word address in the EXAMINE-ON element specifies the remote
node.
The word address in the first GET element specifies the starting address
of the memory access block.
The word address in the second GET element specifies the ending
address of the memory access block.
These elements must be followed by a branch end.
Figure 5.3.B shows the block of words in memory that is now open to
writes from Remote Node 010, due to the memory access branch of
Figure 5.3.A.
Memory access branches can be listed in a single memory access rung.
Note that each group of elements must be preceded by a branch start.
(This is true in all cases, even where only one memory access branch is
defined.) Branch end must be used to fit the memory access rung into the
ladder-diagram display format.
You must end each memory access rung with an Energize Output 02707
element.