A first-setup timeout between an HMI panel and a PLC over Ethernet is almost always the project, not the hardware: the PLC connection is still set for the serial driver the bench test used, or its target address misses the Ethernet module's configured address. Check link lights, addresses, then driver, and prove the fix with a counter value you already trusted over serial.
The fix is usually one setting: open the project's PLC connection, change its driver from the serial driver the bench test used to the Ethernet driver for your PLC family, and set its target to the Ethernet module's configured address, for example 192.168.1.60 under a 255.255.255.0 mask. Two causes cover most first-setup timeouts: that serial driver left in the project, or a target address that misses the module's address. Both are fixed in settings, and the order matters: link lights first, addresses second, driver and target third, then a test against a counter value you already know works over serial. Below you get the symptom list, the checks in that order, a worked bench example with real addresses and ping times, and the test that proves the fix.
What a communication timeout means
A communication timeout is a specific event: the panel's PLC driver sent a request to its configured target and no response arrived before the driver's time limit. The message tells you the exchange failed. Which layer failed is what you diagnose, and there are three: the physical link, the network addressing, and the project's choice of driver and target. On a first setup, the project is where the fault usually sits, because the project was written on the bench, over serial, before the Ethernet hardware existed. A project set for a serial driver keeps using that driver no matter what is plugged into the panel's Ethernet port, and no cable change reaches it. That is why the checks below start with lights and cables and end in the project.
Symptoms and what each one points to
Match your case to one of these and start at its check:
- Timeout from the first download, after a serial bench test that passed. The project's PLC connection still names the serial driver. Go to the driver step.
- No link light at one end of a cable. Power, port or cable. Settings cannot help a dark link; fix the physical layer first.
- A ping from the PC to the module times out. Addressing: the two devices are not in the same subnet, or the address you pinged is not the module's configured address. Go to the address step.
- Pings pass but the panel still times out. The network path is good, so the project's driver or target address is wrong.
- The same tags worked over serial and time out over Ethernet. Driver selection, the usual case on a first move from serial to Ethernet.
- The link passed on the bench and fails after the machine powers up. Supply and boot order, a different job with its own check, linked at the end of this article.
One common panel prints this fault as PLC-001: plc communication timeout; other panels word it differently, and the layer-by-layer order below is the same for all of them.
Check the physical link first
Every port in the path has a link light when it is live: the panel's Ethernet port, the Ethernet module, and each switch port with a cable in it. Lights on both ends of a cable confirm power and connection at that layer; addressing lives above the lights and gets its own check. Plug the panel, the PLC's Ethernet module and the PC into one small switch, one cable per device. A two-device bench, PC straight to the module, also works: ports made in the last two decades negotiate the cable pairing themselves, so a crossed pair is no longer a thing to hunt for. Check the switch's own power light too. A switch that lost its plug is a real cause on a crowded bench, and it costs thirty seconds to look.
Put the PC, panel and module on one switch
The address tool that reads and writes the Ethernet module's address talks over the network, and the panel's programming software downloads the project over the network too. While the PC hangs off the serial programming cable, it can reach neither device. The switch is what puts all three on one network at once, and the serial programming cable stays exactly where it is for ladder work; the switch does not replace it. If the panel also talks to a servo drive over serial, unplug that link until the PLC link passes. A servo link timeout has its own causes, covered in fixing a PLC communication timeout on an HMI servo link.
Match the addresses at both ends
On a bench, use private addresses. RFC 1918 reserves three ranges for networks like this: 10.x.x.x, 172.16.0.0 through 172.31.255.255, and 192.168.x.x, so bench devices never collide with a routed network. Use the common small-network mask 255.255.255.0 and the rule is simple: the first three numbers of the address match on every device in the group, and the last number is different on each one. Read the module's configured address with the address tool named in its documentation, read the panel's address from its network setup, and write both down before you change anything. After every address change, ping the device again from the PC: a healthy reply on a switched bench comes back in single-digit milliseconds, typically under 10 ms, and a timeout reply means the address is still wrong or the cable is not in the network you think it is.
Set the project's driver to Ethernet
This is the step a first setup misses. The project's PLC connection names two things: the driver, which decides which port and protocol the panel speaks, and the target, which decides who it speaks to. Open the project's PLC connection settings and read both. A connection built for the serial bench test names the serial driver for your PLC family, and its target is a serial station or port number. The panel software's help file has a PLC setup section that groups drivers by maker and family; choose the Ethernet driver for your PLC family from there, and enter the module's address from the previous section as the target. Download the project to the panel and watch the screen reconnect. When the same panel also runs serial devices, check the panel driver list before tuning serial settings so the Ethernet connection and the serial connections stay distinct.
Example: a bench setup from first cable to working counter
Scenario: a counter job on the bench. One HMI panel, one PLC with an Ethernet module in its rack, one engineering laptop, one eight-port switch. Bench addresses for the example all use the 192.168.1 range with mask 255.255.255.0:
| Device | Address | Rule check |
|---|---|---|
| HMI panel | 192.168.1.50 | last number unique |
| Ethernet module | 192.168.1.60 | first three numbers match the panel |
| Laptop | 192.168.1.70 | first three numbers match the panel |
Arithmetic: all three addresses start 192.168.1, so with the 255.255.255.0 mask every device sits in one subnet. The last numbers 50, 60 and 70 are all different, so no two devices claim one address. All three fall inside RFC 1918's 192.168 private range.
Network test first. Pinging 192.168.1.60 from the laptop returns in 3 ms; pinging 192.168.1.50 returns in 2 ms; link lights are on at the switch for all three cables. The network layer passes.
The first project download still ends in the timeout, printed as PLC-001: plc communication timeout. Network passes, project fails, so the symptom list points at the driver: the project's PLC connection still names the serial driver from the earlier bench test. Change the driver to the Ethernet driver for this PLC family, enter 192.168.1.60 as the target, and download again.
Result: the counter value on the panel tracks the PLC's counter as it counts, and one preset write, made with the machine in a safe state under the plant's approved procedure, reads back at the PLC. The fix itself is one driver selection and one address; once the addresses are written down, there is nothing left to guess.
Prove the fix with a value you already trust
Use the tags that already worked over serial as the test set. First a live value: the counter value on the panel must change as the PLC counts. A screen that opens is not proof of communication; a changing value is. Then one controlled write, a preset or a reset, made under the plant's approved procedure and confirmed at the PLC in the ladder logic. Once those pass, the Ethernet link is done. For a link that has to live on the machine, add a heartbeat counter so the panel flags a dead link before an operator sees a timeout; the setup of that check is in verify HMI communications with a PLC heartbeat counter.
The order to work in, on the bench and on the machine
Work the list in order and stop at the step that fails:
- Link lights on the panel, the module and every switch port in the path.
- Addresses: first three numbers matching under a 255.255.255.0 mask, last number unique, both ends written down.
- Driver: the project's PLC connection set to the Ethernet driver for your PLC family.
- Target: the project pointing at the module's configured address.
- Test: a live counter value, then one approved write.
Moving from bench to machine changes the addresses, and three places hold one: the Ethernet module, the panel's network setup, and the project's target. Get the address from the group that runs the plant network and update all three together; a bench address in 192.168.1.x times out the moment the panel lands on the plant network. If the link passed on the bench and dies after panel and PLC power up together on the machine, the fault has moved to supply and boot order, covered in fixing a PLC COM timeout after power-up. If reads work and only writes time out, the key switch is the first check, covered in fixing HMI write errors when PLC reads still work.
Recommendation: Bench the whole link before it touches the machine: one small switch, fixed 192.168.1.x addresses with the 255.255.255.0 mask on panel, module and PC, the project's PLC connection moved to the Ethernet driver with the module's address as the target, and the counter value the serial bench test already trusted as the test that shows the link works. When the machine sits on a managed plant network, get the address from the group that runs that network and update module, panel and project target together.
Questions
Does the PLC need to be told that the Ethernet module is installed?
The Ethernet module carries its own network address, read and set with the address tool named in that module's documentation, normally over the network you are building. The panel project then targets that address through its PLC connection. A first-setup timeout comes from those two settings being out of step, the driver or the target, not from the module failing to announce itself. Read the module's configured address, then set the project's target to match.
My laptop has one Ethernet port. How do I reach the panel and the module at once?
One port is enough. Put a small four- or eight-port switch on the bench and run one cable each to the laptop, the panel and the PLC's Ethernet module. The serial programming cable still goes from the laptop to the PLC for ladder work, so program access does not change. What the switch buys you is the PC reaching the module's address tool and the panel's project software at the same time, over the same address range.
What changes when the panel moves from the bench to the plant network?
Three places hold an address and all three must move together: the Ethernet module, the panel's own network setup, and the panel project's target address. Ask the group that runs the plant network for a fixed address inside the machine cell's range and a port on the cell switch. A bench-only address such as one in 192.168.1.x will time out as soon as the panel lands on the plant network, even though the bench test passed.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.