Encountering communication issues with devices can be frustrating. Upon inspecting the PLC cabinet, I noticed that the DeviceNet indicator was flashing E#78 n#1 through 16 on the 1756-EN2T module, which prompted a message indicating to "cycle power to the unit: assert in task idle clock," with the code showing as pc=0x000 0x00021770. When I checked RSLink, I observed that several devices were displaying a red "X" over their modules, and one relay was highlighted in yellow under the dropdown menu for the specified static IP address. Interestingly, I couldn't access this static IP address using Internet Explorer, but I successfully communicated with another DeviceNet system (with a different static IP), which presented no issues and displayed all devices without any red "X" indicators. After cycling the power to the modules, there was no improvement. I then attempted to remove and reinstall the 1756-EN2T module. Currently, the DeviceNet system shows a "NOtx" red flash, while the mod/net light is solid green, and the Ethernet module remains in test mode with a solid red OK LED. My concern is whether the 1756-EN2T module has completely failed, or if there's something else I'm overlooking. Your assistance in resolving this issue would be greatly appreciated. Thank you for your support!
Welcome to the PLCTalk forum community! It's unfortunate that your inaugural post involves a complex issue with multiple modules on the interstate. From what you've described, it appears that you have a system utilizing a 1756 chassis that includes both the 1756-EN2T and 1756-DNB modules, enabling remote access to DeviceNet networks. Generally speaking, it seems that the 1756-EN2T may have experienced a failure. A solid red OK LED typically indicates significant damage. You might want to test the module by placing it in an isolated test chassis to see if it "wakes up." Additionally, it's advisable to remove other modules from the chassis to rule out any interference between them, although this is unlikely to be the case. As for the DNB, it seems to have lost connection to the network previously, but there is also a possibility that it has sustained damage. The absence of transmissions (NoTx) typically indicates that no responses are being received from the network devices.
Thank you for your prompt response and assistance. I initially suspected that the 1756-EN2T module was the source of the problem. The DeviceNet was functioning properly until the original issue arose, resulting in a complete loss of communication. This occurred when the EN2T displayed the message "cycle power to unit assert in task idle clock" along with a solid red LED indicator. Subsequently, DeviceNet reported an E78 error, which seemed logical since it was no longer communicating with the ControlLogix blocks. After removing and reseating the EN2T and cycling power to the system, the NotX issue was resolved.
The 1756-DNB DeviceNet scanner, similar to most other scanners in its category, features an onboard "Scanlist" stored in nonvolatile memory. Unlike simpler devices such as Analog modules, it does not transfer the Configuration assembly from the ControlLogix during the connection setup process. Thus, if the 1756-EN2T fails entirely, the 1756-DNB will simply enter Idle mode, displaying a code 80, which the DNB also indicates when in Idle state. Meanwhile, code 78 signifies "no message reply from the slave device." This issue is rooted in the DeviceNet side of the module and often arises when a device has been disconnected from the network. The "NoTX" status on the 1756-DNB serves as a metaphorical welcome home; you return to find your door ajar and call out, but receive no response. Although it's not as critical as Error 79 (bus-off), it certainly signals the need to investigate why expected replies aren't forthcoming.
You are absolutely right; the system features a 1756 chassis equipped with several key modules: Logix5562, DeviceNet, Ethernet/IP, ProSoft, and relay output. Please find the attached photo for your reference.
Gecco reported that devices have lost communication. Upon inspecting the PLC cabinet, the DeviceNet was flashing error E#78 for units #1 through #16. The 1756-EN2T indicated, “cycle power to unit: assert in task idle clock” with a program counter of pc=0x000 and 0x00021770. Let’s unpack this: DeviceNet error E78 indicates a communication failure with the specified addresses. For example, E78 at #1, E78 at #2, and so forth indicates that while there is a setup for these addresses, the equipment at these locations is unresponsive. I typically monitor scanner #1, hence I'm unfamiliar with the response at #1 E78. When a VFD (Variable Frequency Drive) is turned off and locked out, it will still appear on the scanner as #nn, E78, depending on its specific address. This suggests your power supply is functional since it isn’t reporting a power failure; however, there seems to be a disconnection somewhere within your DeviceNet network. How many devices are currently connected to your DeviceNet? Given that error E78 is listed, there must be communication with at least one other address at this moment. In RSLink, non-functional devices are marked with a red "X" through their modules, and one relay is highlighted in yellow under the static IP dropdowns. I am unable to access this static IP address via Internet Explorer, although I can connect to another DeviceNet network (with a separate static IP) where all devices display properly without any red "X". It's worth noting that the Ethernet card could affect the DeviceNet scanner if the PLC is communicating with both the rack and the DeviceNet card via Ethernet. However, it shouldn't change how the DeviceNet scanner displays information, like the E78 error, indicating that your Ethernet switch appears to be functioning correctly. After cycling power, there were no changes. Furthermore, after removing and reinstalling the 1756-EN2T module, the DeviceNet scanner now shows NOtx with a red flashing status light, while the OK LED is solid green. The Ethernet module appears to be stuck in a TEST state with a solid red OK LED. The NOtx status means the scanner is attempting to poll devices but is receiving no responses. Once again, your power supply is likely fine, but there are issues within the DeviceNet system. Have you lost one or both of your terminating resistors? It is essential to have one terminating resistor at each end of the DeviceNet. You can verify there’s power on the connectors; the red and black wires should read 24V, while terminating resistors should measure across the white and blue wires. Regarding the Ethernet card, removing and reinserting it typically should not cause any damage. If it’s displaying a TEST mode, it might be improperly seated in the rack. Try reseating it to ensure it's connected correctly—it should retain its configuration. If the Ethernet card powers on without its IP address, you may need to re-upload the configuration. If the Ethernet card remains stuck in TEST mode with a RED LED, it is likely malfunctioning and should be replaced. However, I suspect the original issue with the DeviceNet scanner may stem from multiple problems converging at once. Is the 1756-EN2T entirely non-functional, or is there something else I might be overlooking? Thank you for your assistance. Please keep us updated on what you discover next, as these types of issues may require multiple perspectives to resolve.
It sounds like you're really diving deep into this! The flashing E#78 error indicates a module issue, often related to communication faults, which can be tricky to pinpoint. Since you’ve already cycled the power and reinstalled the 1756-EN2T, it's worth checking the cabling and connections to ensure everything's securely attached and not damaged. The fact that you can communicate with another DeviceNet system suggests that the issue might be isolated to this specific setup. If you haven't already, double-check the configuration settings in RSLink to make sure they match what's needed for this module. If the problem persists, it might be time to consider that the module could be faulty, especially if the status indicators remain problematic. Good luck, and keep us posted on what you find!
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Answer: A1: The error code E78 n1 through 16 typically indicates a communication error within the DeviceNet network. It suggests there may be an issue with one or more devices on the network, and further investigation is needed to pinpoint the source of the problem.
Answer: A2: A red "X" indicates a communication error with the module. First, check the physical connections and ensure all cables are securely connected. Then, verify the device configurations and network settings in RSLink. If the issue persists, consider power cycling the affected modules or the entire system.
Answer: A3: Inability to access a static IP address via Internet Explorer may be due to network configuration issues, browser settings, or firewall restrictions. Ensure that the IP address is correct and that there are no network connectivity issues. Additionally, try using a different browser or clearing the cache to see if that resolves the issue.
Answer: A4: A "NOtx" red flash
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