In this article, we will examine the advantages and disadvantages of using ProNET and Network Read/Write (NETW) instructions.

 ProNET

• Description: Productivity’s native peer-to-peer network protocol between Productivity CPUs.
• Advantages:
  • Allows tag-level data sharing between PLCs over Ethernet without custom ladder logic.
  • Each CPU can be configured as a producer (publishing tags) or consumer (subscribing to tags).
  • As single producer CPU can easily publish data to multiple consumer CPUs.
  • Designed for fast, cyclic exchange of data with minimal setup (drag-and-drop tag selection). Cyclic data is transmitted at a fixed interval.
  • Optimized for real-time coordination between multiple Productivity CPUs (e.g., line control, distributed machines).
  • Lower protocol overhead = less network bandwidth consumed per tag
• Disadvantages:
  • Fixed update rate of 10 times per second (100 msec.)
  • UDP broadcast packets publish the blocks of data to the network which limits the scope of the shared data network to the local broadcast domain.
  • Can burden other devices on larger networks. Recommend networks limited to Productivity devices.
  • Data must be in an array tag and the message size for each data type is limited to 128 bytes regardless of the array size defined.
  • Subscribers on the network must have the same data type option selected. Different data types between a subscriber and producer will result in a data type mismatch.
  • A maximum of 32 publishers or subscribers is allowed per project.
  • No serial communication support – Ethernet communication only.

 NETW (Network Read / Network Write)

·       Description: General-purpose explicit message instruction (Auto poll cyclic option is available) to communicate with another Productivity CPU.

·       Advantages:

o  The target IP address or Serial Node can be dynamically changed within the program allowing a single instruction to target different Productivity CPUs with the same setup/configuration.

o  Enables a user to dynamically access different array elements during runtime.

o  Allows a user to manually configure reads/writes of tag data to another Productivity CPU over Ethernet or Serial communications.

o  Can be triggered on demand (by rung conditions) or set to an auto poll cyclic exchange with user defined update rate.

o  Offers fine-grained control: a user can control when, how often, and what data is read/written.

·       Disadvantages:

o  Requires Productivity Series next generation CPUs (such as the P2-622).

o  More overhead per transaction (since the request must carry addressing, etc.)

o  User setup is more involved because configuration of a Productivity PLC Modbus device and NETW instruction(s) are both required.

 In short:

• Use ProNET when networking multiple Productivity PLCs and fast, simple, continuous tag sharing is needed.
  • Example: In industrial settings, using one Productivity CPU as a main alarm annunciator that monitors multiple pump stations.
• Use Network Read/Write for on-demand communication with one or more Productivity CPU(s).
  • Example: PLC that interfaces with SCADA needs to monitor multiple PLCs that control different boiler units. The boiler units are identical and just have different IP addresses. The SCADA PLC can use the same ladder logic to read or write tag values on demand (or cyclically) to and from the different boiler units.