Connecting cMT-G02 to Digital I/O via iR-ETN Modbus TCP

Key architectural rule: iR series I/O modules such as the iR-DM16-P are slice modules that sit on a coupler's local bus. They are not standalone network devices. A cMT-G02 therefore reaches them through a network coupler (iR-ETN family) using the Weintek Remote IO (MODBUS TCP/IP) driver. Only the cMT-CTRL01 gateway can mount iR I/O modules directly on its own side bus, with no coupler in between.

Two Valid Architectures

Option	Topology	When to use
A - cMT-G02 + iR-ETN coupler + iR slice modules	cMT-G02 -> Ethernet switch -> iR-ETN -> iR-DM16-P and other slices	I/O must be remote from the gateway, or you already standardised on the cMT-G02 for its gateway/OPC UA/MQTT role
B - cMT-G02 + iR-ETN40R (integrated I/O coupler)	cMT-G02 -> switch -> iR-ETN40R with 24 DI / 16 relay DO built in	Small point counts; one part number covers coupler and I/O
C - cMT-CTRL01 + iR slice modules	Controller with direct side-bus expansion, no coupler	New design where local I/O is the main requirement and no coupler cost is wanted

Option B is the cleanest starting point for a first build. The iR-ETN40R provides 24 digital inputs, 4 of which are high-speed (20 kHz counter, or 10 kHz A/B encoder on two channels), plus 16 relay outputs. See the iR-ETN40R datasheet.

iR-ETN40R electrical limits to design around

Parameter	Value
Digital inputs	24 DI; 4 high-speed (20 kHz counter / 10 kHz A-B encoder x2)
Digital outputs	16 relay
Relay contact rating	250 VAC / 30 VDC, 2 A per channel
Total output current	8 A max across the module
Relay response time	10 ms
Protocol	Modbus TCP server, up to 8 simultaneous TCP connections
Network	10/100 Mbps, 100 m max copper segment

Step-by-Step: cMT-G02 to iR-ETN Digital I/O

1. Power the rack. Feed 24 VDC to both the cMT-G02 (accepts 10.5-28 VDC) and the coupler. Use a supply sized for the coupler, all slice modules and field sensor loads, then verify the field-side 24 V return is bonded per your panel's grounding scheme.
2. Assemble the I/O. Clip the iR-DM16-P (or other slice modules) onto the iR-ETN's side bus in the physical order you intend to address. Slot order determines the Modbus register offsets, so record it before you close the panel.
3. Cable the network. The cMT-G02 has a single Ethernet port. Run cMT-G02 -> managed or unmanaged switch -> iR-ETN. Keep each copper segment under 100 m. Do not daisy-chain the I/O through a PC NIC or a Wi-Fi bridge for control traffic.
4. Set the coupler IP. Assign a static address in the same subnet as the cMT-G02, e.g. gateway 192.168.1.10, coupler 192.168.1.20, mask 255.255.255.0. Avoid DHCP for I/O nodes; a lease change silently kills the poll.
5. Add the driver in EasyBuilder Pro. In the cMT-G02 project, create a new device and select the Weintek Remote IO (MODBUS TCP/IP) driver. This driver understands the iR module layout and exposes the slices as named I/O rather than raw registers.
6. Configure connection parameters. Set the coupler IP, TCP port 502, and the unit/station ID expected by the coupler. Confirm the module list in the driver matches the physical slot order from step 2.
7. Map the tags. Bind bit objects, macros or logging entries to the DI and DO addresses generated by the driver. Digital inputs map to read-only coil/discrete-input space; digital outputs map to writable coils.
8. Download and cycle power on the gateway, then on the coupler, so the coupler completes bus enumeration before the first poll arrives.

Addressing and Protocol Notes

If you choose to use a generic Modbus TCP master instead of the Weintek Remote IO driver, you lose automatic slot mapping and must work in raw register space. In that case:

Function	Modbus operation	Typical use
Read digital inputs	FC02 (Read Discrete Inputs) or FC01 depending on coupler mapping	Sensor states from DI slices
Write digital outputs	FC05 (Write Single Coil) / FC15 (Write Multiple Coils)	Relay or transistor output slices
Read analog / status words	FC03 / FC04	Counters, module diagnostics

Verify the exact register base and per-slot offset against the coupler's manual before commissioning. Guessing the offset produces the classic failure mode of correct comms but I/O bits landing one slot away from where you expect.

Verification and Commissioning Checks

1. Link layer: confirm the coupler's Ethernet LED shows link and activity. No activity with link up usually means an IP/subnet mismatch.
2. IP reachability: ping the coupler from a laptop on the same switch. If ping fails, fix addressing before touching the EasyBuilder project.
3. Port 502: open a Modbus test client and read one known discrete input. Success here proves the coupler is serving before the gateway is blamed.
4. Input proof: jumper a field input to 24 V and watch the corresponding bit in the cMT-G02 project change state. Walk every DI point once during commissioning; wiring transpositions are far more common than driver faults.
5. Output proof: force each DO from the gateway with the field load disconnected, and confirm contact continuity with a meter. Then reconnect loads and re-test one group at a time while monitoring total output current against the 8 A module ceiling.
6. High-speed inputs: if you use the counter or encoder channels, verify the pulse source is within 20 kHz (counter) or 10 kHz (A/B encoder) and check the count register increments monotonically at full machine speed, not just at hand-turn speed.
7. Loss-of-comms behaviour: unplug the coupler cable and confirm the outputs go to the state your process requires. Configure the coupler's fault/watchdog output behaviour deliberately; do not accept the default without testing it.

Troubleshooting Matrix

Symptom	Likely cause	Action
No I/O data, gateway shows comm error	IP/subnet mismatch, or DHCP lease change on coupler	Set static IP on coupler in the gateway's subnet; verify mask
Comms OK but wrong points toggle	Slot order in driver does not match physical assembly	Re-enumerate module list against physical slice order
Intermittent dropouts	Cable run over 100 m, poor termination, or shared Wi-Fi path	Move I/O polling to wired 10/100 link; re-terminate; keep segments under 100 m
New client cannot connect, gateway fine	8 TCP connection limit reached on coupler	Close idle engineering sessions; consolidate clients behind the gateway
Relay outputs chatter or weld	Inductive load without suppression, or total current above 8 A	Add flyback diode (DC) / RC snubber (AC); re-budget simultaneous ON current
Outputs will not pulse fast enough	10 ms relay response floor	Use a transistor output slice for fast switching instead of relay outputs
iR module mounted directly on cMT-G02	Unsupported - no local expansion bus exists	Insert an iR-ETN coupler, or migrate to cMT-CTRL01

Choosing Between cMT-G02 + Coupler and cMT-CTRL01

Pick the cMT-G02 path when the device's primary job is protocol gateway, data collection and remote access, and the I/O simply needs to be visible on the same network. Pick the cMT-CTRL01 when the device's primary job is local control of iR slices: it mounts the modules directly and removes the coupler, its IP address, its power feed and one more failure point from the bill of materials. Mixing both is legitimate - a cMT-CTRL01 with local I/O can still be polled by a cMT-G02 acting as the plant-facing gateway.