ProtoLink developed a DDE server to communicate with Allen-Bradley PLCs using
the DF1 protocol. The server was designed specifically to support a packaging
room management application utilized by a major snack food manufacturer. It
performs high-speed polling for real-time production information and
periodically logs collected data to an Oracle database. Examples of data logged
include totals for packaging machine downtime, case counts, eye spots, and
foreign matter detection events.
A handshaking scheme is implemented in the PLCs and the DDE server to ensure
that counter data is not lost due to timing issues. The server supports
communication with both the PLC-5 and SLC models from Allen-Bradley. This
special-purpose server also provides a mechanism for adding generic PLC
registers to its addressable namespace during configuration without requiring
code modifications.
