The Ebyte JGD121-EM11 is an industrial EtherCAT-to-Modbus protocol conversion gateway that exchanges data between an EtherCAT fieldbus and Modbus TCP or Modbus RTU devices, supporting Modbus master, slave and transparent transfer modes over two RJ45 EtherCAT ports (IN and OUT), one dedicated Modbus TCP RJ45 port and one 3.81mm terminal RS485 interface, with a bus cycle as fast as 1~4 ms on the EtherCAT side, a 10 ms minimum cycle on Modbus TCP, 2400~6M bps on Modbus RTU, DC 8~28V supply with reverse-polarity protection and galvanic power isolation, and a 55x30x80mm housing on a standard 35mm DIN rail for -40~+85 degC industrial service.
Key Features & Advantages
- Three Protocol Worlds In One Module: The gateway speaks standard EtherCAT on the fieldbus side and both Modbus TCP and standard Modbus RTU on the serial / Ethernet side, so an EtherCAT master such as a TwinCAT or Beckhoff PLC can read and write registers held by Modbus instruments, inverters and remote I/O without a separate protocol computer or PC-based driver.
- Modbus Master, Slave And Transparent Transfer: Beyond plain register mapping, the device can act as the Modbus master polling a bus of RTU slaves, as a Modbus slave exposing its EtherCAT process data, or as a transparent bridge, which is what lets the same part serve both new EtherCAT designs and brownfield retrofits where the Modbus device list is fixed and cannot be re-addressed.
- EtherCAT with IN and OUT Ports: Two 100M RJ45 ports give a true EtherCAT daisy chain, so the gateway sits inline at the end of a drop cable instead of consuming a dedicated master port. The ECAT indicator exposes the real EtherCAT state machine (INIT off, Pre-OP fast flash, Safe-OP slow flash, OP steady) so a commissioning engineer can read the bus state at the panel without a laptop.
- 1~4 ms Bus Cycle Against a 10 ms Modbus Floor: The EtherCAT side runs as fast as 1~4 ms depending on master configuration and device count, while the Modbus TCP side has a 10 ms minimum cycle and Modbus RTU runs 2400~6M bps with 8 data bits, 1/2 stop bits and None/Odd/Even parity. That asymmetry is the real design constraint, and it is why the mapping must be planned around a stable data snapshot rather than a per-cycle handshake.
- Industrial Power Input And Protection: DC 8~28V covers the 12V, 24V and 48V control-voltage families found in cabinets, drawing 2~3W, with a red PWR indicator and documented reverse-polarity protection. The RS485 pair is brought out as A / B / G terminals plus a separate PE earth terminal, which is the correct way to bond a shielded bus without circulating ground current through the signal reference.
- Field-Serviceable By Design: The Reload button performs three documented actions - a short press under 2 seconds reboots, a 5~10 second hold restores factory settings, and holding while powering up enters firmware upgrade mode - and the SYS and ERR lamps signal upgrade progress. Ebyte also publishes a parameter configuration tool and the ESI file so the device can be imported directly into an EtherCAT master configuration.
Core Specifications
Compiled from the JGD121-EM11 official performance parameter, indicator lamp and interface definition tables. Cells marked [to be confirmed] are not published on the product page and must be taken from the JGD121-EM11 user manual before design freeze.
| Category | Item | Specification |
|---|---|---|
| Product | Type / role | EtherCAT gateway - EtherCAT to Modbus conversion |
| Protocols | Supported | EtherCAT, Modbus TCP, Modbus RTU |
| Protocols | Modbus roles | Modbus master, Modbus slave and transparent transfer |
| Power | Working voltage | DC 8~28V (V+ / V- on 3.81mm terminals) |
| Power | Power consumption | 2~3W |
| Power | Protection | Power isolation with reverse-polarity protection |
| EtherCAT port | Interface | RJ45 x 2 - EtherCAT IN and EtherCAT OUT |
| EtherCAT port | Bus cycle / bandwidth | Fastest 1~4 ms (depends on master config and device count); 100M |
| Modbus TCP | Interface / cycle / bandwidth | RJ45 dedicated port; minimum cycle 10 ms; 10/100Mbps auto-sensing |
| Modbus RTU | Interface / baud rate | RS485 on 3.81mm terminal (A / B / G); 2400~6M bps |
| Modbus RTU | Frame format | Data bits 8; stop bits 1/2 (default 1); parity None/Odd/Even (default None) |
| Indicators | Lamps provided | PWR (red), SYS (blue), ERR (red), ECAT (blue), TCP (green), RTU (green) |
| Controls | Reload button | Factory reset: hold 5~10 s powered on. Reboot: press under 2 s. Firmware upgrade: hold while powering up |
| Environment | Operating / storage | -40~+85 degC, 5%~95%RH non-condensing / -40~+105 degC, 5%~95%RH non-condensing |
| Mechanical | Dimensions / weight | 55 x 30 x 80 mm (L x W x H, excluding terminals); 140 ± 5 g |
| Mechanical | Mounting | Standard industrial 35mm DIN rail |
| Software | Published resources | User manual, parameter configuration tool, ESI file for master import |
| Mapping | Register map size / object dictionary | [to be confirmed - see user manual] |
| Mapping | Max Modbus RTU slaves polled | [to be confirmed - see user manual] |
| Isolation | Rated isolation voltage | [to be confirmed - isolation is stated, the rated voltage is not] |
| Certification | EMC / safety certificates | [to be confirmed - not stated on the product page] |
| EtherCAT | Jitter / distributed clocks | [to be confirmed - see user manual] |
Product Selection Guide
Notice for Selection: The JGD121-EM11 is a wired industrial Ethernet gateway - it contains no radio, so no ISM band, antenna or RF certification question applies to this model; the checks that matter are protocol-side. First confirm your EtherCAT master can import the published ESI file and that a 1~4 ms bus cycle suits your motion or I/O scan requirements. Second confirm which Modbus role your site needs: this is a single-order-point product (one EtherCAT-to-Modbus gateway, no variants), so if your application requires a different protocol pair (for example PROFINET or a remote I/O node rather than a protocol gateway) it belongs to a different Ebyte product family and should be confirmed before ordering. Third, verify the register mapping and slave count your project needs against the JGD121-EM11 user manual, since the map size is not published on the product page.
| Wiring / integration decision | How the JGD121-EM11 handles it | What you must confirm |
|---|---|---|
| EtherCAT daisy chain, gateway inline at the end of the drop | EtherCAT IN from the upstream device, EtherCAT OUT to the next node or terminated | Master cycle time and device count, since 1~4 ms depends on both |
| Existing Modbus TCP instrument or HMI on the plant LAN | Dedicated Modbus TCP RJ45 port, 10/100Mbps, 10 ms minimum cycle | Whether the gateway or the peer is the Modbus TCP client in your scheme |
| Legacy RS485 sensor or meter bus | RS485 A / B / G on 3.81mm terminals, 2400~6M bps, Modbus RTU | Slave addresses, parity and stop-bit settings, and the maximum slave count in the manual |
| Cabinet with 12V, 24V or 48V control voltage | DC 8~28V input, 2~3W, reverse-polarity protected, isolated supply | 48V nominal systems exceed 28V and are outside the stated range |
| Need to expose EtherCAT data to an unrelated Modbus TCP SCADA | Modbus slave mode publishes the process data as holding registers | Register map layout from the manual, and scan rate versus the 10 ms floor |
Industrial Installation & Wiring
1. Mechanical: Clip the 55x30x80mm housing onto a standard 35mm DIN rail. The quoted dimensions exclude the terminals, so allow the terminal depth plus cable bend radius at the front, and keep neighbouring devices clear of the RS485 and power terminal block so a screwdriver can reach it during commissioning.
2. Power: Feed DC 8~28V to the V+ and V- 3.81mm terminals. The supply is isolated and reverse-polarity protected, but it is still correct practice to fuse the branch and to keep the 2~3W load on a rail shared with relays or contactors away from the noisy coil side. The red PWR lamp confirms the internal rail is up.
3. RS485 bus: Connect A to A, B to B and G to the common reference of the trunk, and bond the cable screen at one end to the PE terminal. Run the bus as a single daisy chain rather than star or tapped branches, set 8 data bits with the stop bits and parity the slaves expect (default 1 stop, No parity), and start at a conservative baud rate before raising toward the 2400~6M bps ceiling, because long or poorly terminated RS485 runs fail at high baud long before the transistors reach their limit.
4. Ethernet: EtherCAT IN receives the drop cable from the master or the previous node, EtherCAT OUT continues the chain. The Modbus TCP port is separate and must not be bridged into the EtherCAT segment - the whole point of the third port is that the two networks stay physically isolated and only the gateway moves data between them.
5. Read the lamps before you open a laptop: ECAT steady blue means OP, slow flash Safe-OP, fast flash Pre-OP, off INIT. SYS steady blue means the device has entered OP; a 500ms slow flash means it has not; off means an operating fault. ERR lit is an EtherCAT communication error. On TCP and RTU, a 200ms fast flash means normal traffic, a 1s slow flash means the channel is enabled but idle, and a 3s steady lamp indicates a communication error on that channel.
6. Commissioning and firmware: Use the published parameter configuration tool to set the Modbus role, mapping and serial parameters, and import the published ESI file into the EtherCAT master so the module appears with the correct process-data description. For firmware work, hold Reload while powering up to enter upgrade mode - SYS and ERR flash together slowly in the upgrade wait state and fast at 0.5s during writing. A 5~10 second hold once running restores factory settings, so record your mapping first.
Practical Application Scenarios
1. Bringing Legacy Modbus Meters and Drives onto a New EtherCAT Line
A machine builder retrofitting an EtherCAT-based line usually keeps the installed Modbus instruments: energy meters, soft starters, VFDs and torque controllers that cannot be re-protocolled. The gateway polls those RTU slaves and republishes their values as EtherCAT process data, so the PLC program sees ordinary inputs and outputs instead of a serial driver, and the 1~4 ms bus cycle keeps the motion-side scan unaffected by the slower serial side.
2. Exposing an EtherCAT Cell to Modbus TCP SCADA or an HMI
Plant SCADA, energy dashboards and third-party HMIs are overwhelmingly Modbus TCP. Running the gateway in Modbus slave mode turns the cell process data into holding registers on the dedicated TCP port, so the supervision system reads it without ever touching the EtherCAT network - a clean security and stability boundary as well as a protocol convenience.
3. Substation, Water and Environmental Telemetry Cabinets
Unattended cabinets aggregate RS485 flow, water-quality and weather sensors under Modbus RTU and hand the data upstream over EtherCAT to a controller or edge gateway. The -40~+85 degC rating, 5%~95%RH non-condensing tolerance, isolated DC 8~28V input and PE-bonded bus make the part usable in unheated kiosks, and the per-channel TCP and RTU lamps let a technician confirm which link died without instrumentation.
4. Test Rigs and Batch Equipment with Mixed Vendor Buses
A test bench frequently mixes a TwinCAT or Beckhoff controller with cheap Modbus power supplies, loads and environmental chambers. Transparent transfer mode passes Modbus requests across the EtherCAT side without the master having to model every register, which shortens integration on one-off equipment where the register documentation is thin and the commissioning window is short.
FAQ Section
Q1: What is the practical difference between Modbus master, slave and transparent transfer on this gateway?
Master mode means the gateway itself initiates requests, so it polls your RS485 or Modbus TCP slaves on a schedule and places the answers into EtherCAT process data - use it when the other devices are dumb responders. Slave mode means the gateway exposes its own registers and something else polls it - use it for SCADA or HMI reads. Transparent transfer passes Modbus frames through without the gateway interpreting every register, which is what you want during commissioning or when the peer device has a non-standard map. Pick the mode first, because it determines how you write the PLC or SCADA side.
Q2: The ECAT lamp is flashing slowly - is the device faulty?
No. The ECAT lamp mirrors the EtherCAT slave state machine: off is INIT, fast flash is PRE-OP, slow flash is SAFE-OP and steady is OP. A slow-flash device has been detected by the master but has not been moved to OP, which is usually a master-side condition - the XML / ESI description does not match the firmware, the expected process-data length differs, or the master has not issued the SAFE-OP to OP transition. Check the master state and the ESI file version before suspecting hardware, and cross-read SYS, which is steady blue only in OP.
Q3: Can I put this gateway on a 48V DC control supply?
No. The stated working range is DC 8~28V, which covers 12V and 24V nominal systems with headroom and, with care, 48V logic supplies that are actually sitting near 24V - but a genuine 48V rail exceeds the specified maximum. Use a DC-DC isolating converter to feed the module 24V, or select a product rated for the 48V family. Note also that a 24V rail derived from an unregulated rectifier under charge can ride above 28V, which is the more common way this input gets over-voltaged in the field.
Q4: Why does my Modbus side look slower than the EtherCAT side, and does that matter?
It is expected and it is a design input, not a fault. EtherCAT is a fast, deterministic on-the-fly copy at 1~4 ms, while Modbus TCP carries a 10 ms minimum cycle here and Modbus RTU is bounded by baud rate, slave turnaround and frame length. The gateway therefore samples or refreshes Modbus data at Modbus speed and publishes it to the bus at EtherCAT speed. Size your application around that: use the EtherCAT side for values the control loop consumes, do not build a control loop that waits on a Modbus round trip inside one bus cycle, and if you need faster serial data, raise the baud rate, shorten the trunk or split the slaves across two buses.
