Connect a C-More panel to any Modbus RTU device

The roles on the link

The panel is the master, also called the client. It starts every read and every write. Scroll the same dropdown and you find no Modbus slave driver for the panel itself, so the panel cannot be the answering end. Three consequences:

• Your device is the slave. It sits at a slave address you set in the device, and the panel's driver setup points at that address.
• The device cannot push. If a value changes, the panel sees it on its next poll of that tag. A state latched inside the device needs a register the panel can poll.
• Modbus RTU carries one master per link. A second polling device on the same pair of wires collides with the panel, so poll the device from one master.

This is the same role split as connecting an HMI over Modbus RTU when no listed driver fits.

What you need

• The device's Modbus register table: address, register type, data format, scaling.
• The device's serial numbers: baud rate, parity, stop bits, slave address.
• A cable wired from the pin tables in both manuals. RS-232 crosses transmit and receive; RS-485 lands on the A/B pair. It is the same wiring job as puting a Modbus RTU HMI on a legacy PLC serial port.
• Optionally a serial monitor or the device's request log, which turns questions about commands into readings.

Pick the driver and match the serial numbers

1. In Panel Manager, select Modicon Modbus RTU. The manufacturer's driver setup documentation shows the screens the selection opens.
2. Set the panel's port to the device's numbers, read from the device manual. If both ends are configurable, the Modbus serial-line default of 19200 baud, 8 data bits, even parity, 1 stop bit is the common meeting point. Many devices ship at 9600 baud with no parity; whatever the device is fixed at, the panel moves to it.
3. Point the driver at the device's slave address. Address 1 is the factory default on most Modbus devices; confirm it in the device, because a wrong slave address fails every tag at once.
4. Set Registers Per Message to 1 and Coils Per Message to 1. Those two settings cap how many registers or coils one message may carry; at 1, every request stays single-register and single-coil.
5. Save the project and wire the port before the first download.

If your target is a listed PLC instead of a generic device, how to set the PLC type in Panel Manager covers that path.

Map one holding register

The read test is one numeric object and one tag. Use a display-only object first so nothing you touch can write into the device.

1. Drop one numeric display object on a screen and enter a new tag name. The tag Name - Add window opens.
2. Choose the serial device dEV001, or whatever the serial device is named in your project.
3. Set tag Data Type to Unsigned Int 16. That is the right type when the register holds one unsigned 16-bit value, which most holding registers do.
4. memory Type offers only 4. That 4 is the holding-register area, which is why the address drops its leading 4.
5. Type the address from the device table with the leading 4 removed: the table's 40001 is typed as 0001.
6. Apply, download the project, and put the panel on the wire.

Example: reading holding register 40001 from a device at slave address 1

Inputs: the device's table lists 40001 as an Unsigned Int 16 holding register whose current value the device's own tool or front panel shows. Both serial ends run the Modbus serial-line default, 19200 baud, 8 data bits, even parity, 1 stop bit. The device sits at slave address 1, its factory default. Registers Per Message is 1 from the setup steps.

The rule: a 4xxxx table number is the area digit 4 glued to the register number, and memory Type 4 in the tag already carries the area digit.

The arithmetic: 40001 = area digit 4 + register 0001, so the tag address is 0001. One Unsigned Int 16 tag is one 16-bit register, so the panel asks for quantity 1. A second tag on adjacent register 0002 makes two requests of quantity 1 each while Registers Per Message is 1; raised to 8, the same pair can travel as one request of quantity 2.

The result to demand: the number on the panel equals the value the device shows for that register, and it follows a deliberate change at the device on the next poll. Watch the object for 30 seconds after the change so you see at least a few poll cycles.

The decision: that equality is the gate. Pass it and build the screen; fail it and stay at one tag, because every extra tag adds a variable to a link that has not read one register yet. Work addressing and serial numbers first, using the sequence for Modbus RTU no-reply and address errors.

Write commands you pick, read commands you test

The Modicon Modbus RTU setup gives you four write choices: 06 writes one register, 16 writes several, 05 writes one coil, 15 writes several. Pick per the device's documented command list. Reads have no selector: the panel chooses the command from the object type, and which code it uses per object is not published. The protocol side is fixed: function code 03 reads holding registers and 04 reads input registers, per the Modbus specification. With memory Type 4 as the only slot, your readable values must exist as holding registers; a value the device publishes only as an input register has no slot in this mapping, so look for a holding-register mirror of it in the device manual.

Plan on single writes. One register per write, command 06, until a test on a safe register shows a multi-register write arriving whole.

Choose the write-test register so a wrong value cannot move the machine or the process. That is the one place this job carries real risk.

How to check it worked

One change at a time, so a failure names its own cause:

1. One known register reads and tracks a change. That is the example above.
2. Add a second address, only after the first passes.
3. Put two adjacent registers on one screen. If single reads pass and the pair fails, keep Registers Per Message at 1 permanently for this device; grouping of contiguous tags is not published, and 1 removes the question.
4. Add one write object on a register that is safe to change, with command 06 selected. Confirm the new value lands in the device. If the write lands and the next read times out, that pattern has its own fix in recovering from a Modbus RTU timeout right after a write.
5. Test each data type your screens use as its own case. One passing Unsigned Int 16 display tells you nothing yet about a 32-bit pair or a scaled value; test those as their own cases.
6. If a serial monitor is on the link, read the requests out of it: function code, slave address, register address, quantity. That answers "which read command does it use" on your hardware, for your object types.

Recommendation: pick Modicon Modbus RTU for any Modbus RTU device that is not on the PLC list, run the panel as the only master on the link, hold Registers Per Message at 1, and gate the project on one holding register reading the right value at the device's slave address. Raise the message size only when the device manual documents multi-register reads, and add write objects only after the read path passes.

Questions