Allen-Bradley Generic EtherNet/IP Setup |
Topic: CM210 |
The Allen-Bradley EtherNet/IP Server (Generic IO Messaging) (Control/CompactLogix) protocol is different from all other protocols that we have on C-more panel in that the panel is a Server (Slave) to communications instead of the Client (Master).
C-more supports two types of communications using the ODVA ( www.odva.org ) generic EtherNet/IP protocol:
- CIP Implicit I/O Messaging using the Generic Ethernet Module setup in ControlLogix and CompactLogix I/O configuration.
- CIP Explicit Messaging using the CIP Generic Message Type inside of ControlLogix and CompactLogix MSG instructions.
In both of these methods, the C-more panel is the Ethernet Server (Slave) and the CompactLogix or ControlLogix PLC is the Ethernet Client (Master). As of January 2006, only the ControlLogix Ethernet modules (1756-ENBT and 1756-ENET/B) and CompactLogix Controllers with Ethernet supported this type of messaging. PLC5 Ethernet, SLC 5/05, MicroLogix 1100 and 1761-NET-ENI are not supported by C-more's Allen-Bradley EtherNet/IP Server (Generic IO Messaging) (Control/CompactLogix) driver. To communicate to the SLC5/05, MicroLogix 1100(1400) + 1761-NET-ENI use the appropriate Client driver.
Benefit of EtherNet/IP
The generic EtherNet/IP server protocol works well (very fast) for connectivity between (1) PLC Client (Master) and (1) C-more Panel Server (Slave) or (1) PLC Client (Master) and multiple C-more Panel Servers (Slaves), but it is much more difficult to connect multiple PLC Clients (Masters) and 1 or more C-more Panel Servers (Slaves).
Implicit Messaging
EtherNet/IP Implicit I/O Messaging writes output Data and reads input Data constantly as fast as possible. This is different from most HMI panel connectivity in that most devices read constantly but only write upon change of value or on events. This is obviously a problem with multiple PLC Clients (Masters) because each Client will be constantly overwriting the other. Therefore, Implicit I/O Messaging works well with (1) PLC Client (Master).
Generic EtherNet/IP Implicit Messaging Setup
Explicit Messaging
It is probably better to not use EtherNet/IP if the application requires one HMI panel and multiple PLC. But if it must be used, use of Explicit Messaging is possible.
When using Explicit Messaging, the user will have to control both, the PLC reads and writes of Data to and from the panel. Reading constantly is no problem and can be accomplished in a relatively easy fashion. Writing Data is a little more difficult. There are two hurdles to overcome when doing this:
- Writing the Data only when it changes so that you are not constantly overwriting what the other Masters may be changing.
- Write only the changed Data and not the unchanged data.
To accomplish #1, the user must write the PLC Ladder Logic to check to see when a particular register has changed. Once the user has determined that one of the register’s Data values has changed, then they need to accomplish #2.
To accomplish #2, the user will need to read back the other unchanged values from the panel (because one of the other values may have been changed by one of the other Masters) and then write the changed Data and unchanged Data back to the panel. This is commonly known as a Read/Modify/Write.
