The subnet mask and default gateway exist even when the panel's front screen shows only an IP address. Set all three in the panel programming software under Setup > Touch Panel Network > Ethernet Port, put controller and panel on one subnet with unique addresses, and treat a green link with dead tags as a protocol driver fault.
The mask and the gateway are not missing. The panel's front screen shows one IP address, but the panel still stores a subnet mask and a default gateway, and you set all three in one place: the panel programming software, under Setup > Touch Panel Network > Ethernet Port. Give the controller and the panel unique addresses on the same subnet, with the same mask, and the link comes up. When the link is up and the tags stay dead, the fault has moved to the protocol driver, and editing addresses will not reach it.
The three settings live in one tab
The controller's network setup asks for three values: IP address, subnet mask and default gateway. The panel's front screen asks for one, which reads as if the other two do not exist. They do. Open the panel programming software on your PC and go to Setup > Touch Panel Network > Ethernet Port. That tab holds a static IP address, a subnet mask and a default gateway. Every Ethernet port you configure there needs its own unique address on the network.
Two more places hide the same values. The controller keeps its three in its own module setup, so read them there first. When a project transfer from the PC to the panel fails, open the network adapter settings on the PC and check its subnet mask as well: a laptop outside that subnet fails the transfer.
What each value decides
IP address. The device's own address, unique across the whole network. Two devices sharing one address break communication for both.
Subnet mask. Splits the address into a network part and a host part. 255.255.255.0 keeps the first three octets as the network and leaves 8 bits for devices. That is 2^8 = 256 addresses, minus the network address and the broadcast address, so 254 usable addresses per subnet.
Default gateway. The router that carries traffic to addresses outside the local subnet. On a cable with two devices it moves nothing. On a plant network it is the way out, so take it from the plant addressing plan.
Symptoms and what each one points to
- No link light on either port. Cable, port or switch. Fix the physical link first; addresses come after. Keep the whole run inside the 100 m limit for one Ethernet segment before you suspect the addresses.
- Link light on, ping fails. Addressing. A wrong mask on one end, or one address used twice.
- Ping passes both ways, tags stay dead. The network is done. The protocol driver and the controller-side connection settings are the fault. This is the case where the ping passes but the reads fail.
- Worked on the old controller family, dead on the new one. The project still points at the old family's driver. Pick the driver for the new controller first; check the protocol before replacing a legacy HMI walks that choice.
- The front screen shows only an IP. Nothing is missing. The mask and the gateway sit in the Ethernet Port tab.
Check the addresses with arithmetic
One comparison tells you whether two devices can talk locally. With mask 255.255.255.0, the first three octets are the network, and both addresses must show the same first three octets. 192.168.1.10 and 192.168.1.20 share 192.168.1 and reach each other directly. 192.168.1.20 and 192.168.5.10 share only 192.168, so with that mask each sits outside the other's subnet and the panel hands that traffic to its gateway.
Confirm the path with timings, not just link lights. Ping with a 1000 ms timeout: on a healthy direct link or one switch hop, both devices answer in under 1 ms. A reply stretched to 100 ms or more on a two-device cable points at a duplex mismatch or a failing port, not at the addresses.
Duplicates are quieter. Ping the address you plan to assign before you assign it. On an isolated bench, a silent address is free. On a plant network, take addresses from the plan's owner.
If the network runs DHCP, read the address the controller actually received before you compare anything. The value on an old printout is stale.
Example: one controller, one panel, one subnet
Scenario: bench setup before the cabinet build. One controller, one panel, one programming laptop, one switch, patch leads under 5 m each.
| Device | IP address | Subnet mask | Gateway |
|---|---|---|---|
| Controller | 192.168.1.10 | 255.255.255.0 | 192.168.1.1 |
| Panel | 192.168.1.20 | 255.255.255.0 | 192.168.1.1 |
| Laptop | 192.168.1.30 | 255.255.255.0 | 192.168.1.1 |
The mask gives 24 network bits and 8 host bits: 2^8 = 256 addresses, minus 192.168.1.0 for the network and 192.168.1.255 for broadcast, leaves 254 usable, .1 through .254. All three devices sit inside. The laptop pings 192.168.1.10 and 192.168.1.20 with a 1000 ms timeout and both answer, each in under 1 ms. Link lights on. The project loads with the driver for the controller family, and the tags animate.
Now one change: move the controller to 192.168.5.10 and leave the panel at 192.168.1.20. The panel's subnet is 192.168.1.0 and 192.168.5.10 sits outside it, so the panel sends that traffic to its gateway. There is no gateway on a bench, so the ping at 1000 ms times out. The link light stays green and the tags die. Same devices, same cable, one octet.
The fix, in order
- Read the controller's IP address, mask and gateway from its own setup screens.
- In the panel programming software, open Setup > Touch Panel Network > Ethernet Port.
- Set the panel's static address on the controller's subnet, one address away, with the controller's mask and the plan's gateway.
- Apply the settings to the panel. Both link lights come on.
- From a laptop on the same subnet, ping the controller, then the panel, with a 1000 ms timeout. Both must answer in under 1 ms on a bench link.
- Open the project's controller setup and confirm the driver matches the controller family. Pings good, tags dead: fix the driver here and stop editing addresses. An Ethernet connection timeout on a first setup walks that path in detail.
- Write the three values on the panel's install sheet.
Straight-through or crossover
Through a switch, use a straight-through patch lead. That is the standard arrangement. Direct from panel to controller, a straight-through lead also works when either port supports automatic crossover, which covers current panels and controllers. Try a crossover lead only when a direct link light stays dark.
The decision
Recommendation: Put controller and panel on one /24 subnet: mask 255.255.255.0 on both, unique addresses such as 192.168.1.10 and 192.168.1.20, one gateway from the plant plan, all set in Setup > Touch Panel Network > Ethernet Port. If the link is up and both devices answer a ping while the tags stay dead, the network is correct: change the protocol driver to the one documented for your controller family.
After the link is up
Record the three values with the panel and close the question. If the same floor also wants a notice board that plays its own content, shop-floor signage is a separate and simpler job from the HMI link.
Questions
My panel's screen only asks for the IP address. Where are the subnet mask and gateway?
In the programming software. The front screen shows one field, but the panel stores all three values. Open Setup > Touch Panel Network > Ethernet Port on the PC and you get the static IP address, subnet mask and default gateway fields together. Set the mask to the controller's mask, normally 255.255.255.0.
Should the panel use the same IP address as the controller?
No. A duplicate address breaks communication for both devices. Give each a unique address on the same subnet: 192.168.1.10 for the controller and 192.168.1.20 for the panel, both with mask 255.255.255.0. The first three octets match, so each device reaches the other without a router.
When does the default gateway matter on this link?
When traffic leaves the local subnet: a programming PC on another network, a plant data collection server, remote support. On a cable carrying only the controller and the panel, the gateway moves no traffic. Set it anyway, from the plant addressing plan, so the value is already right on the day the panel joins a larger network.
The link light is green but the tags will not update. Is the subnet mask wrong?
Probably not, once both devices answer a ping. A green link with dead tags points at the protocol driver or the controller-side connection settings. Open the project's controller setup, confirm the driver matches the controller family, and correct that before touching the addresses again.
Do I need a crossover cable between the panel and the controller?
Through a switch, no: a straight-through patch lead is the standard arrangement. Direct between the two devices, straight-through works when either port supports automatic crossover, which current panels and controllers do. Keep one crossover lead in the kit for the direct link whose light stays dark.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.