PLC-5 Typed Read MSG: Data from Control Logix to PLC5

[Mike Carter]

Hello All, I want to read data from a Control Logix PLC, into a PLC5/60, using Ethernet and a MSG instruction in the PLC5. When verifying the MSG instruction in the PLC5, I get an error message. "Target Address in invalid". Once I figure out how to do this I need to replicate it in another PLC5. Scope is to read the status of 4 paint pumps controlled by the CLX. If any of the 4 stop, the PLC5 needs to know, because it is controlling the paint application equipment. Source data resides in a Control Logix 1756-L63. The tag is INT type, 4 elements long, and the name is PUMP_STS_B2. The IP address of the CLX is 4.2.6.230. There are 2 ENBT cards, one in slot 1, and the other in slot 3. 4.2.6.230 is slot 3. PLC2,5 / SLC Mapping has been created in the CLX. File=421 Name PUMP_STS_B1 and File=422 Name Pump_STS_B2. The file mappings represent a binary file created in each of the PLC5's B421:0~4 in Booth 1, and B422:0~4 in Booth 2. The PLC5/60 is Enhanced series E model using the Ethernet side card. The IP address of the PLC5 is 3.26.5.61. I also created MG file types in each of the PLC5/60. MG420:0~19 in each processor. This was necessary to use the MSG instruction in the PLC5. I have searched the forums for examples of how to do this with no solid results. I am trying to follow the best practices of reading the data into my PLC so anyone who follows can tell where it is coming from. While the IP addresses are not closely related they should be able to communicate. I say this because all of our PC's are on the 4.2.6.XXX network on a 255.255.252.0 sub net and we have no issue communicating with the 3.26.5.61 IP address. Any help and advice would be greatly appreciated. Regards, Mike Carter

[Ken Roach]

The "Multi-Hop" feature tells the PLC-5 and 1785-ENET to use the ControlLogix CIP protocol and allows you to tell it which Slot number of the 1756 chassis the ControlLogix CPU is in. First, you need to verify that the PLC-5/60 and the 1785-ENET sidecar can support the CIP protocol used by ControlLogix. There's a good Knowledgebase document on the RA site, # 7983. The 1785-ENET needs to be Series A Rev D or higher, or any Series B. I'm not sure what the firmware dependency for the PLC-5 controller itself in your situation will be. RSLogix 5 might tell you by implication; see if it allows you to select Multi-Hop. The PLC-5 doesn't know about ControlLogix tags at all; it's emulating a PLC-5 data table. You need to put a PLC-5 style address in the Target Device Data Table Address field. When your PLC-5 requests B422:0, length 4, it will get a reply from the ControlLogix containing the value of PUMP_STS_B2[0] through [3]. With regard to the IP addresses, there's definitely a gateway device somewhere in there. It's a basic fact of IP subnetting that a device with an address of 4.2.6.XXX with a subnet mask of 255.255.252.0 cannot communicate with a device with a 3.26.5.61 IP address because the subnet mask requires that the first two octets be identical (mask 255), and they are not. This is probably a very old network, maybe from before the Internet, because it's considered a capital offense among IT folks to use a globally routable IP address on an internal network.

[Mike Carter]

Hello Ken, The sub net mask for the side card 3.26.5.61 IP address is 255.0.0.0. The gateway is 3.26.1.100. It does predate the Internet. The gateway for the 4.2.6.xxx is 4.2.4.1. I changed the IP address on the side card via an Ethernet connection and things went south in a hurry. Because I didn't want to disrupt our start up tomorrow night, I connected to the PLC5 with a Laptop and in program mode put it back to the original settings. Changing the IP address will be something for another day, because some RSLINX topics will need to be updated. I guess from a networking perspective I need to get with my IT guys. We are using domain controllers, and VLANS but I am not quite sure how all of our computers on the 4.2.6.xxx network can communicate with the old 3.26.5.xxx stuff. Regardless, I need to change the IP addresses on both of the PLC5's to the same set up as everything else. Aside from the IP conflicts, I am pretty sure my hardware is up to date on the PLC5 side. It is a 5/60 Enhanced Series E, Rev E.2. The 1785-ENET is a B. Does everything else look normal?

[Ken Roach]

Even with a wide-open Class A network where the subnet mask is 255.0.0.0, the device on the "3" network has to go through a gateway to get to the "4" network. And that's fine, if there is a Default Gateway address configured in both PLC-5 controllers so they know where to send their off-network messages. The MSG instruction will need the "Multi-Hop" feature enabled and configured so that it goes to the correct Slot number in the remote ControlLogix chassis. You'll also have to change the "Target Controller Data Table Address" as I described to a PLC-5 style address, not a ControlLogix tag name.