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Is there a guideline to go by when messaging? I have over 100 message read instructions. Can I execute them all at once? Should I stagger them? What is the deciding factor to consider? |
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The program I am working on reads messages from 10 other PLCs. I am currently using the staggering method. Basically, msg read 1 executes on first scan, when msg read 1 is done or error, unlatch the trigger bit for msg read 1 (previously latched by the PLC first scan bit) and latch the trigger bit for msg read 2. Continue with this process until msg read 100 is done or error and unlatch the trigger for msg read 100 and latch the trigger for msg read 1. According to Rockwell, the recommended number of message instructions executing at the same time should be 5, so messages should be grouped and sequentially executed so that no more than 5 message intructions are executing. Other good practices - use produced/consumed tags for data that needs to be there fast (however uses CIP connections in ENBT), and consolidate data so that you are only reading once or twice from each controller. |
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To quote Peter Nachtwey's answer:
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These worksheets may help. I think we got the info from Rockwell documentation: EtherNet/IP TCP/IP Requirements PLC Worksheet Each EtherNet/IP application should be reviewed for its TCP/IP connection requirements. The following worksheet will assist in determining the number of connections required for each Allen-Bradley PLC within the system. TCP/IP Connections (for each PLC in the system) RSLogix connection to the PLC using EtherNet/IP (enter 1 here) How many RSLinx or 3rd Party OPC/DDE Servers? How many PAC devices will be accessed via an unconnected MSG instruction? How many other (Non Opto 22) EtherNet/IP devices? How many Logix to other EtherNet/IP PLC TCP/IP connections? How many remote PLCs will connect to this PLC using a TCP/IP connection? How many Generic Ethernet Modules are defined? Total Number of TCP/IP connections (sum the “Quantity” column together) Depending on the specific PLC or EtherNet/IP module, your application could exceed the TCP/IP connection resources. If this should happen for users of ControlLogix, additional EtherNet/IP modules may be used. Typically, ControlLogix modules may support 64 (1756-ENBT) or 128 (1756-EN2T or 1756-EN2F) TCP/IP connections. CompactLogix typically supports 32 connections. Please see Allen-Bradley form “enet-um001_-en-p.pdf” for the specific TCP/IP limitations of your PLC. MicroLogix PLC’s such as the 1100 and 1400 support 8 TCP/IP connections. An SLC-5/05 supports 64 TCP/IP connections. These limits are described in each product’s published specifications. EtherNet/IP Multicast Requirements PLC Worksheet Each EtherNet/IP application should be reviewed for its multicast requirements. The following worksheet will assist in determining the number of connections required for each Allen-Bradley PLC within the system. Multicast Connections (for each PLC in the system): How many “Generic Ethernet Modules,” with status? x 2 How many remaining “Generic Ethernet Modules?” How many consumed tags to other EtherNet/IP PLC’s? How many produced tags to other EtherNet/IP PLC’s? Total Number of Multicast Connections (add ”Total” column together) This total reflects the total number of CIP connections required for the application. Use the latest version of the “EtherNet/IP Capacity Tool” to accurately determine limits of your application. This is only necessary in applications that have large numbers of I/O especially when PLCS themselves are producing and consuming tags. Please note that only some of the ControlLogix EtherNet/IP modules support implicit messaging. The modules that support implicit messaging are the 1756-ENBT, 1756-EN2T and the 1756-EN2F EtherNet/IP modules. |
