Ethernet is not the only path between this panel and PLC. The panel software lists a serial driver for the PLC family: select it on the DEV001 device under SETUP, wire the maker's documented cable from the panel to the CPU's RS-232 RJ12 port, and copy the PLC port's four serial values onto the panel. A register that moves on a test screen confirms the link in both directions.
Ethernet is one option for this panel and PLC, and it is not the only one. The CPU in this family carries an RS-232 port on an RJ12 jack, and the panel project software ships a serial driver written for that PLC family. Pick the driver on the panel's first serial device, wire the maker's documented cable between the two ports, and set the same serial values at both ends. This page walks the setup in the order you meet it: driver, cable, settings, and the test that shows live data. The example hardware is a 15-inch EA7-T15C panel and a Do-more CPU, but the path holds for any panel whose software lists a serial driver for your PLC.
Is Ethernet the only way to connect an HMI to this PLC?
No. The CPU's RS-232 port on its RJ12 jack carries the same tags as the network link once the panel project names the PLC maker's serial driver on device DEV001 and the maker's documented cable joins the two ports.
Two conditions have to hold at once. The panel software must list a driver for the PLC family, and the CPU must expose the serial port. For this pairing both are true: the C-more software offers Automation Direct Do More serial in its protocol list, and the Do-more CPU's programming port is RS-232 on an RJ12 jack. That combination is the whole permission slip for a serial link.
When the driver list stops short of your PLC, the fallback is a generic protocol the PLC can also speak; connecting a Modbus RTU HMI to a legacy PLC's RS-232 port covers that route. The same serial-versus-Ethernet choice comes up on computers too, and connecting a PC HMI to a PLC over serial or Ethernet walks it from the PC side.
What do you need before touching the panel settings?
Five things: the panel project software on a PC with your project file, the panel model, the PLC CPU model with its port list, the maker's matched cable, and both manuals opened at their serial settings pages.
While you gather parts, read the port list in the CPU documentation and confirm the RS-232 RJ12 port is on your exact model; families mix port layouts between generations. The cable for this pairing is marked EA-2CBL. Have it in hand before the day of the work; hand-wiring an RJ12 plug onto an RS-232 line is how good setups go bad.
How do you select the PLC's serial driver in the panel software?
Open the project, select SETUP, choose the panel type, open COM Port, click DEV001, open PLC Protocol, and pick the PLC maker's serial driver from the drop-down; six clicks, in that order.
- Open the project in the C-more software and select SETUP.
- Select the panel type from the drop-down menu, EA7-T15C in this example.
- Select COM Port on the left side.
- Click DEV001. The protocol selection opens.
- Click PLC Protocol.
- Pick Automation Direct Do More serial from the drop-down menu, then save the project.
The project then travels from the PC to the panel the way your projects normally do. Until that transfer finishes, the panel keeps whatever driver it had.
If the drop-down has no entry for your PLC family, check the version of the panel software before anything else; driver lists grow between releases. Checking the panel driver list before tuning serial settings covers that step in depth. Do not fill the gap with a similarly named Ethernet driver or a generic serial driver; a generic driver has no map for this PLC's registers.
Which cable joins the panel to the RS-232 RJ12 port?
The maker's own serial cable, marked EA-2CBL for this panel and CPU family; RJ12 plugs that fit are easy to buy, and the wiring inside them follows each maker's own conductor assignment.
RJ12 is a 6-position modular connector. RS-232 needs at least transmit, receive and signal ground, and makers land those on their own pins, so the cable is a matched part, not a commodity. A plug that fits the jack does not establish the wiring is right; read the part marking on the cable before it goes in.
Length is the other cable number. The original RS-232 standard set its line guidance at 50 ft (15 m) for speeds up to 20 kbit/s, and that figure still plans well. At 38400 baud or faster, keep the run shorter and route it away from drive cables. A panel on the same cabinet as its PLC has no length problem at all.
Make and break this cable with the panel powered down and the machine in a safe state; a repinned plug that lands voltage on the wrong conductor can damage a port.
The driver and cable are right, so why is there still no data?
Because the two ends are probably not set to the same speed and framing; read the PLC port's settings first and copy them onto the panel's serial device.
Four values have to match: baud rate, data bits, parity, stop bits. The most common factory default on PLC serial ports is 9600 baud, 8 data bits, no parity, 1 stop bit, so test that combination first when you have nothing else to go on. Ports get changed in the field, so confirm at the PLC, in its programming software or its manual, before you trust a default. Some PLC ports carry fixed serial values at the PLC end; connecting an HMI to a PLC port with fixed serial settings covers that case.
| What the panel shows | What that points to | The check that separates it |
|---|---|---|
| Communication fault, no data at any time | Driver or cable | Confirm DEV001 still names the PLC serial driver, and read the cable's part marking |
| Project downloads, tags sit at zero | Settings mismatch | Read the four values at the PLC port and compare the panel device |
| One tag updates, another stays blank | Tag address, not the link | Open the silent tag in the project and compare its address with the PLC register |
What does a finished example look like from SETUP to a moving value?
A 15-inch panel on a cabinet door, a Do-more CPU 12 ft below it, one EA-2CBL cable, and four serial values copied from the PLC into the panel project; that is the whole job, and it ends with a number moving on a test screen.
The run is 12 ft of cable against the 50 ft (15 m) planning figure, so length leaves 38 ft of margin and the cable is not the variable. In the project: SETUP, panel type EA7-T15C, COM Port, DEV001, PLC Protocol, Automation Direct Do More serial. The EA-2CBL cable joins the panel's serial port to the CPU's RJ12 jack.
Then the settings. For this example the PLC port reads 19200 baud, 8 data bits, even parity, 1 stop bit. Those four values are example inputs; your PLC port hands you its own numbers when you read it, and the read is the step that matters. The same four values go onto the panel's DEV001 device.
Transfer the project, then put one register on a test screen. Toggle the PLC-side input that feeds the register, and the panel number follows. Then one write test: a button on the panel sets a bit, and the bit appears in the PLC programming software. Both directions moving, the machine goes back to service.
How do you confirm the link before the machine goes back to service?
Watch one value change in both directions: a register the PLC moves and the panel shows, then a bit the panel writes and the PLC sees; the download path runs PC to panel, so it leaves the panel-to-PLC link untested.
- Power the panel and watch its communication indication for the state your manual calls healthy.
- Read one register on a test screen, move its PLC-side input, and see the panel follow.
- Write one bit from the panel and see it in the PLC software.
- Walk the real screens: every tag you plan to display, and every button you plan to press.
Recommendation: keep the link serial when the panel sits within 50 ft (15 m) of the PLC and you hold the maker's cable; it is one less switch, one less network setup and one less address to document. Use the Ethernet port when the run is longer, when the panel shares the PLC with other devices, or when the cabinet is already networked. Choose Ethernet for reach or for sharing, and fix the serial path where it stands: the driver on DEV001, the cable marking, then the four settings.
Questions
How far can an RS-232 cable run between a panel and a PLC?
Treat 50 ft (15 m) as the planning number, which comes from the original standard's guidance at speeds up to 20 kbit/s. Past that distance, or at high baud rates in a noisy cabinet, use the Ethernet port or a short-haul converter instead of a longer serial cable.
What should you write down before calling the panel maker's support line?
Six items: the panel model, the PLC CPU model, the protocol named on DEV001, the cable part marking, the four serial values read at the PLC port, and the exact wording of the panel's communication indication. That one sentence answers the first round of questions support will ask.
Does moving the link to Ethernet fix a serial fault?
No. Ethernet is a different interface with its own driver and its own settings, so it sidesteps the fault without removing it. Correct the serial path where it stands: driver on DEV001, cable marking, then the four values. Choose Ethernet for reach or for shared access, with the serial link retired on purpose.
What if the protocol list has no entry for the PLC family?
Update the panel software first, because driver lists grow between releases. If the entry is still absent after the update, give the PLC's serial port a protocol both ends speak, such as Modbus RTU where the port supports it, or plan on the Ethernet port. Do not select a generic driver and hope the register addresses line up.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.