User`s manual

ioLogik E1200 Series Using ioSearch
4-12
Active OPC Server—From Pull to Push
When looking up an I/O devices’ Modbus table, 19 or more steps are required to create a single tag. The steps
include specifying the IP address, selecting the protocols, and defining the data type. The procedure is repeated
over and over again until all the devices and tags are created. It takes about 1 minute for a user with a technical
background to create one tag. But what if there are 400 tags in an OPC system? Not only does it take a long
time to configure such a large number of tags, it also puts a heavy load on the CPU.
OPC also requires the connected I/O devices to use fixed IP addresses. This type of architecture is sometimes
referred to as “pull” technology, because the OPC server always needs to pull data (by “polling”) from the I/O
devices for tag creation, IP connection, and tag status updates.
Moxa’s ioLogik Active Ethernet I/O products offer I/O status reports via TCP/UDP messaging, e-mail, and SNMP
traps. In addition, they now support OPC technology. An ioLogik can automatically generate tags without
requesting any data or even a device’s IP address. All the user needs to do is launch the Active OPC Server
program, and the I/O channels selected by the user will be “pushed” from the ioLogik to the Active OPC Server.
The “push” technology also includes the update for the tags. When the I/O status changes, the ioLogik will send
updates to the Active OPC Server. Compared to polling the status (the so-called pull-based method), this
feature efficiently reduces network bandwidth usage and speeds up response time with event-driven,
push-based status updates. At the same time, the heartbeat function monitors the system’s basic signs of life.