Max IEC Gateway user manual

1. Introduction

Max IEC Gateway is a protocol converter. It reads values from Modbus devices and gives them to a SCADA system that speaks IEC 60870-5-104 (over TCP/IP) or IEC 60870-5-101 (over a serial line). Commands from the SCADA system go back to the Modbus devices.

The gateway runs as a service on a Windows or Linux computer. There is no desktop program: you configure everything in a web browser, in the dashboard.

What the gateway can do

• Read Modbus TCP, Modbus RTU (RS-485/RS-232) and Modbus RTU over TCP devices. Several devices can share one serial line.
• Serve the data as an IEC 60870-5-104 server (several masters at the same time) and/or an IEC 60870-5-101 outstation.
• Single and double points (also from bits inside a register), step positions, 32-bit bitstrings, measured values (normalized, scaled, float) and energy counters (integrated totals), with or without CP56 time tags.
• Commands: single, double, set-points (normalized, scaled, float) and bitstrings, written back to coils or holding registers. Select-before-operate or direct execute.
• Deadbands, cyclic transmission, event buffering while no master is connected, clock synchronization.
• 9 device templates, CSV import/export, a traffic monitor, trends and a historian.
• Every change applies immediately. You never need to restart the service to apply a setting.

Words used in this manual

The glossary at the end explains every term. The most important ones:

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2. Requirements

Network ports

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3. Installation

Windows: installer (recommended)

1. Download MaxIECGateway_Setup_1.1.1.exe from the download page.
2. Run the file. Windows asks for administrator rights: click Yes.
3. Follow the wizard. On the Select Additional Tasks page you can choose:
   • Allow the web dashboard (TCP 5000) from the local network: tick it if you want to open the dashboard from other computers. Without it, the dashboard works only on the gateway computer.
   • Allow IEC 60870-5-104 (TCP 2404) from the network: tick it so SCADA masters on other computers can connect.
   • Create a desktop shortcut (web dashboard): optional.
4. Click Install. The installer creates and starts the Windows service Max IEC Gateway (service name MaxIECGateway).
5. At the end, leave Open the web dashboard ticked and click Finish. Continue with First start.

Windows: portable ZIP

1. Download MaxIECGateway_Portable_1.1.1.zip and unzip it to a folder, for example C:\MaxIECGateway.
2. Double-click MaxIEC.Gateway.exe. A console window opens and shows the log.
3. Open http://localhost:5000. The gateway runs as long as the window is open.

Linux (x64, systemd)

1. Download maxiec-gateway_1.1.1_linux-x64.tar.gz to the Linux computer.
2. Unpack it and run the installer as root:

   tar -xzf maxiec-gateway_1.1.1_linux-x64.tar.gz
   cd maxiec-gateway-1.1.1
   sudo ./install-linux.sh

3. The script installs the program to /opt/maxiec-gateway, creates the service user maxiec, gives it access to serial ports (group dialout or uucp) and starts the systemd service maxiec-gateway.
4. Open http://<linux-host>:5000 in a browser. From another computer you need the setup code: sudo cat /var/lib/maxiec-gateway/setup-token.txt.

sudo systemctl status maxiec-gateway     # is it running?
sudo systemctl restart maxiec-gateway    # restart
sudo journalctl -u maxiec-gateway -f     # live log

Upgrading from version 1.0

• Run the new installer over the old version. You do not need to uninstall first.
• The gateway now runs as a Windows service. The old autostart at logon is removed.
• Your database, license key and trial record are copied to the new data folder C:\ProgramData\MaxIECGateway (Linux: /var/lib/maxiec-gateway). The original files are not deleted.
• The dashboard now needs a password. Set it on the first visit (see First start).
• Your license key keeps working.

Uninstalling

Windows: Settings → Apps → Max IEC Gateway → Uninstall. The service and the program files are removed. Your data folder C:\ProgramData\MaxIECGateway (database, license, trial record, password) is kept, so a later installation continues with the same configuration and license. Delete the folder by hand if you want to remove everything.

Linux: stop and disable the service (sudo systemctl disable --now maxiec-gateway), then delete /opt/maxiec-gateway and /etc/systemd/system/maxiec-gateway.service. The data in /var/lib/maxiec-gateway stays until you delete it.

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4. First start: set the password

The dashboard is protected by a password for the user admin. On the first visit you choose this password.

1. On the gateway computer, open http://localhost:5000 in your browser.
2. The page Set the dashboard password opens.
3. Type a password with at least 10 characters in both fields.
4. Click Set password and log in. The dashboard opens.

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1. 11. New password (at least 10 characters).
2. 22. Repeat the password.
3. 33. Set the password and log in.

Setting up from another computer

If you open the dashboard from another computer for the first time, the page also asks for a Setup code. This protects a new gateway on the network. The code is in the file setup-token.txt in the data folder (Windows: C:\ProgramData\MaxIECGateway, Linux: /var/lib/maxiec-gateway) and in the gateway log. Or simply open http://localhost:5000 on the gateway itself.

Logging in

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1. 11. User name: always admin.
2. 22. Your password.
3. 33. Log in.

• A login stays valid for 60 minutes without activity. Then you must log in again.
• After 5 wrong passwords within 15 minutes, logins from that address are blocked for 15 minutes.

Changing the password

Click Change password at the top right of any page. Enter the current password and the new one twice. Other browsers that are logged in are signed out.

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Forgot the password?

1. On the gateway computer, stop the service (Windows: Services → Max IEC Gateway → Stop; Linux: sudo systemctl stop maxiec-gateway).
2. Delete the file admin.json from the data folder.
3. Start the service again and set a new password on the first-start page.

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5. Dashboard tour

After login you see the Dashboard. It shows the state of the IEC servers, the Modbus devices and every data point.

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1. 11. Menu: Dashboard, Devices, Mappings, Traffic, Trends, Settings, License.
2. 22. Status bar: license state and whether the gateway is bridging (shown on every page).
3. 33. Change password and Log out.
4. 44. IEC 104 and IEC 101 server state, and a summary of devices and data points.
5. 55. Device Connections: each enabled device, its address, Connected/Disconnected and the last communication. Disable/Enable switches polling off and on.
6. 66. Live Data Points: every mapped point with its Modbus address, IEC type, IOA, raw value, scaled value, quality and age.

The status bar

Quality column

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6. Modbus devices

A device is one Modbus slave (one unit ID) that the gateway polls. Open the Devices page.

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1. 11. Add from template: create a device with all its points from a ready-made template.
2. 22. Add Device: create an empty device.
3. 33. Per device: Edit, Mappings (opens its point list) and Delete (also deletes its mappings).

Add a Modbus TCP device

1. Click Add Device.
2. Enter a Name, for example Energy meter feeder 2.
3. Keep Transport = Modbus TCP.
4. Enter the IP address / host name and the TCP port (normally 502).
5. Enter the Unit ID (slave address) of the device.
6. Check poll interval, timeout and retries (see the table below).
7. Click Save. Polling starts at once.

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1. 11. Name of the device (shown everywhere in the dashboard).
2. 22. Transport: Modbus TCP, Modbus RTU over TCP or Modbus RTU (serial).
3. 33. IP address or host name.
4. 44. TCP port (default 502).
5. 55. Unit ID (slave address).
6. 66. Poll interval in milliseconds.
7. 77. Timeout for one request.
8. 88. Retries before the device counts as not answering.
9. 99. Enabled: untick to stop polling this device.

Add a Modbus RTU (serial) device

1. Click Add Device and choose Transport = Modbus RTU (serial).
2. Choose the Serial port from the list or type it, for example COM3 or /dev/ttyUSB0.
3. Set Baud rate, Parity, Data bits and Stop bits exactly as on the device.
4. Enter the device's Unit ID and click Save.

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1. 11. Transport: Modbus RTU (serial).
2. 22. Serial port (COM3, /dev/ttyUSB0 …).
3. 33. Baud rate.
4. 44. Parity: None, Odd or Even.
5. 55. Stop bits: 1 or 2.
6. 66. Unit ID: must be different for every device on the same port.
7. 77. Inter-frame delay: 0 = automatic.

Add a Modbus RTU over TCP device

Use this for a serial device server (Ethernet-to-RS-485 converter) that passes raw RTU frames over TCP. Choose Transport = Modbus RTU over TCP and enter the converter's IP address and port. Devices with the same address and port share one connection, and requests are sent one at a time.

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1. 11. Transport: Modbus RTU over TCP.
2. 22. IP address of the serial device server.
3. 33. Its TCP port (often 4001 or 502).
4. 44. Hint: devices behind the same converter share one connection.

Add a device from a template

A template creates the device and all its mappings in one step. Templates included:

1. Click Add from template.
2. Choose the Device type. Read the yellow notes: they tell you the factory settings and what to check.
3. Enter the device name, transport and address, and the unit ID.
4. Check Common address and First IOA. The points get consecutive IOAs starting at the first IOA. The gateway suggests the next free IOA.
5. Click Create device.

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1. 11. Device type (template).
2. 22. Notes: factory settings and what to verify.
3. 33. Transport.
4. 44. Address of the device.
5. 55. Common address of the points.
6. 66. First IOA: the points are numbered from here.
7. 77. Create the device with all mappings.

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7. Point mappings

A mapping connects one Modbus value to one IEC point. Open Mappings. Choose a device at the top to see only its points.

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1. 11. Device filter.
2. 22. Add Mapping.
3. 33. Export CSV: download the mappings as a CSV file.
4. 44. Import CSV: import many mappings at once (chapter CSV import and export).
5. 55. Report: the deadband (±) and the cyclic time of the point.
6. 66. Per mapping: Edit and Delete.

The mapping dialog

Click Add Mapping (or Edit). The dialog has four parts: Modbus, IEC 60870, Scaling and Reporting.

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1. 11. Device the value is read from.
2. 22. Description (shown in the dashboard and the traffic monitor).
3. 33. Modbus Data Type: Coil, DiscreteInput, InputRegister or HoldingRegister.
4. 44. Modbus Address, 0-based (see below).
5. 55. Register Type: how the register(s) are decoded.
6. 66. Byte Order for 32- and 64-bit values.
7. 77. IEC Type ID.
8. 88. IOA of the point.
9. 99. Common Address (CA).
10. 1010. Scale Factor (and Offset).
11. 1111. Deadband mode.
12. 1212. Deadband Size.
13. 1313. Cyclic every (s).

Modbus data type and address

Register type and byte order

The Register Count is set automatically to what the register type needs. The Signed box is only for old 1.0 mappings: for new ones choose Int16 instead.

A 32-bit value uses two registers with 4 bytes, called A B C D from the most significant byte. Devices send them in different orders:

For 64-bit values the same rule applies to all four registers (CDAB reverses the register order). 16-bit values ignore the byte order. If a float shows nonsense like 1.4E-41 or -2.6E+38, try CDAB. More help: Modbus float byte order guide.

Which IEC Type ID for what?

IOA must be unique within a common address. Its maximum depends on the IOA size in Settings (3 bytes: 1-16,777,215). The Common Address is normally 1 (1-65534 with a 2-byte CA).

Scaling

The gateway calculates: value sent = raw value × Scale Factor + Offset. For commands it calculates the other way round.

Points from register bits

Many devices pack alarms and states into one status register. Use Bit (ON) and Bit (OFF) (0 = least significant bit, −1 = not used):

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1. 11. Data Type: HoldingRegister or InputRegister (bits are only possible from registers).
2. 22. Register Type: UInt16 (bits 0-15) or a 32/64-bit type (bits 0-31 / 0-63).
3. 33. Bit (ON): the bit number. Bit (OFF) stays −1.
4. 44. Type ID: a single point (M_SP_*).

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1. 11. Bit (ON): the bit that means ON (closed).
2. 22. Bit (OFF): the bit that means OFF (open).
3. 33. Type ID: a double point (M_DP_*).

Interrogation group

Interr. Group 0 means the point is sent only in a station interrogation (QOI 20). With 1-16 the point is also sent when the master asks for that group (QOI 21-36). For energy counters, groups 1-4 are the counter groups.

Deadband and cyclic transmission

Measured values (M_ME_*) are sent spontaneously (cause 3) when they change. The deadband reduces traffic for values that change all the time:

• A general interrogation always returns the current value, whatever the deadband.
• Cyclic every (s): also send the point every n seconds with cause 1 (periodic). 0 = off. Allowed: 0-86400.

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8. Commands from SCADA

A command point lets the SCADA master write to a coil or holding register. To create one, make a mapping and tick Command.

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1. 11. Data Type: Coil or HoldingRegister (inputs are read-only).
2. 22. Register Type and byte order of the target register.
3. 33. Type ID that matches the command (see table).
4. 44. The IOA the master sends the command to.
5. 55. Command ticked.

• The time-tagged versions (C_SC_TA_1 … C_BO_TA_1, types 58-64) are accepted and handled like the plain ones.
• A command point is also read and reported like a normal point, so the master sees the current value.
• Set-points that do not fit the register type are rejected, never cut off.
• Regulating step commands (C_RC_NA_1) are not supported and are rejected.

Select-before-operate and direct execute

Choose the command mode in Settings → Command Options:

The Select timeout (s) is 10 s by default (1-60 s). A deactivation (cause 8) cancels a pending select. Bitstring commands have no select bit and always execute directly.

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1. 11. Command Mode: Direct Execute or Select Before Execute.
2. 22. CMD Act. Termination: send ACT_TERM after single/double commands.
3. 33. CSE Act. Termination: send ACT_TERM after set-points.
4. 44. Select timeout (s).

What the master sees

Why was my command rejected?

A rejected command gets a negative confirmation (P/N bit set). The Traffic page shows the reason.

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9. IEC 104 settings

Open Settings. All settings apply as soon as you click Save Configuration. A change that makes connected masters reconnect (for example a new port) asks you first.

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1. 11. Enabled: switch the IEC 104 server on or off.
2. 22. TCP Port (default 2404).
3. 33. Max Connections: masters at the same time (1-64, default 10).
4. 44. Allowed masters: IP addresses or networks that may connect.

• Allowed masters: for example 10.0.0.5, 192.168.1.0/24. Empty = any address. It applies at once: connected masters that are no longer allowed are disconnected. This computer (localhost) is always allowed.
• Several masters can be connected at the same time. Each gets all data and can send commands.

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Timers and windows (APCI)

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10. IEC 101 settings

IEC 60870-5-101 uses a serial line (RS-232 or RS-485). Tick Enabled in the IEC 101 card and set the line exactly like the master.

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1. 11. COM Port, e.g. COM1 or /dev/ttyS0.
2. 22. Baud Rate (default 9600).
3. 33. Link Address of the gateway.
4. 44. Link Mode: Unbalanced (master polls) or Balanced (both sides may send).
5. 55. Link Addr Size: 0, 1 or 2 bytes.
6. 66. Master link address (balanced mode only).
7. 77. Parity: Even is the FT 1.2 standard.

• The ASDU sizes (COT, CA, IOA) from the ASDU card are used for IEC 101 too. Many IEC 101 systems use COT 1 byte, CA 1 byte, IOA 2 bytes: check your master.
• The Event buffer size applies to IEC 101 too; changing it restarts only the IEC 101 link.
• Changing the port or any line setting restarts only the IEC 101 link. IEC 104 keeps running.

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11. Time tags and clock synchronization

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1. 11. Time tags in local time (the SU bit is set in summer time). Off = UTC (default).
2. 22. Mark time tags invalid (IV) until a master has synchronized the clock.
3. 33. What a clock synchronization command (C_CS_NA_1) does.

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12. Energy counters and counter interrogation

Energy registers (kWh, kvarh, pulse counts) are mapped as integrated totals: Type ID M_IT_NA_1 (15) or M_IT_TB_1 (37).

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1. 11. Register Type of the counter, e.g. UInt32, Int64 or Float32.
2. 22. Type ID M_IT_NA_1 or M_IT_TB_1.
3. 33. Interr. Group: counter group 1-4 (0 = general only).

• Counters are not sent in a general interrogation and not on every change. The master reads them with a counter interrogation (C_CI_NA_1, type 101).
• The value sent is a 32-bit integer (−2,147,483,648 … 2,147,483,647) after scaling. Choose the scale factor so the value fits, e.g. Wh → kWh with scale 0.001.
• Each reading carries a sequence number, a carry bit (the counter went backwards, e.g. after a rollover), an adjusted bit and an invalid bit.

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1. 11. Event buffer: events kept while no master is connected (10-100000, default 1000). When it is full, the oldest are dropped.
2. 22. Periodic counter report (s): freeze and send all counters every n seconds (0 = only on counter interrogation).

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13. CSV import and export

With CSV files you can prepare hundreds of points in Excel and import them in one step.

1. On Mappings, click Export CSV to get a file in the right format (or start from the example below).
2. Edit the file in Excel or a text editor. Comma or semicolon separated; a decimal comma is accepted.
3. Click Import CSV and choose the file.
4. Optional: choose one device (all rows go to it) and/or tick Replace the devices' mappings.
5. Click Check file. The gateway checks every row and shows a preview. Nothing is saved yet.
6. If there are errors, fix them in the file and check again. When the file is valid, click Import.

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1. 11. Choose the CSV file.
2. 22. Target: the devices named in the file, or one device.
3. 33. Replace: delete the devices' current mappings first.
4. 44. Check file: validate and preview.
5. 55. Result of the check.
6. 66. Import: saves all rows (only active when the file is valid).

Columns

Example file

device,description,modbusType,address,registerType,byteOrder,iecType,ioa,ca,scale,deadbandMode,deadband
Meter feeder 2,Feeder 2 current [A],InputRegister,10,Float32,ABCD,M_ME_NC_1,120,1,1,Absolute,0.5
Meter feeder 2,Feeder 2 voltage [V],InputRegister,12,Float32,ABCD,M_ME_NC_1,121,1,1,Percent,1
Meter feeder 2,Feeder 2 breaker,Coil,8,UInt16,ABCD,M_SP_TB_1,122,1,1,None,0
Meter feeder 2,Feeder 2 energy [kWh],HoldingRegister,80,UInt32,ABCD,M_IT_NA_1,123,1,1,None,0

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14. Traffic monitor, trends and history

Traffic monitor

The Traffic page shows what happens on both sides of the gateway. It is the first place to look when something does not work.

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1. 11. Tabs: Commands, Connections, Modbus, IEC; the badge shows the number of entries.
2. 22. Auto-refresh every 3 s (switch off to read calmly).
3. 33. Clear the list.

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Trends

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1. 11. Choose one or more data points (hold Ctrl to select several).
2. 22. Time range: 1 h, 6 h, 24 h or 7 days.
3. 33. Load Chart.
4. 44. Export CSV: the history of all selected points for the chosen time range, in one file (one row per stored value, with columns for time, IOA, device, point, value and quality).

Historian settings

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• Historian Enabled: record the values of all points.
• Recording Interval: 1 s to 1 h (default 2 s). Values are stored when they change, and at least every 5 minutes.
• Retention Period (hours): 1-8760 (default 72 h = 3 days). Older data is deleted.

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15. Live changes: what restarts what

You never need to restart the gateway to apply a change. Only the part that is affected restarts:

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16. Connecting a SCADA master or test tool

Any IEC 60870-5-104 master can connect: a SCADA system, an RTU, or a test tool. Use these settings in the master:

1. Make sure the gateway shows IEC 60870-5-104 Running on the Dashboard and the status bar is not red.
2. On a different computer, the Windows firewall must allow port 2404 (installer option) and the master's IP address must be allowed in Allowed masters (or the list must be empty).
3. Connect the master. It sends STARTDT; the gateway confirms.
4. Send a general interrogation (C_IC_NA_1, CA 1, QOI 20). You receive all points, then the activation termination.
5. Watch the Traffic page: the Connections tab shows the master's IP address.

Example: switching IOA 201 with select-before-operate

Assume IOA 201 is a command point on a coil (M_SP_NA_1 + Command) and the command mode is Select Before Execute.

If your tool asks for raw ASDU bytes (type, VSQ, COT 2 bytes, CA 2 bytes, IOA 3 bytes, SCO):

Select ON:   2D 01 06 00 01 00 C9 00 00 81
Execute ON:  2D 01 06 00 01 00 C9 00 00 01
Select OFF:  2D 01 06 00 01 00 C9 00 00 80
Execute OFF: 2D 01 06 00 01 00 C9 00 00 00

(201 = C9 00 00; the last byte is the SCO: bit 7 = S/E, bit 0 = state.)

Testing without hardware

Use the slave simulator of ModbusBB as a Modbus device and any IEC 104 test tool as the master. This is how the screenshots in this manual were made.

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17. License

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1. 11. License Status: trial or licensed, licensed to, device name, machine ID, last online check, and the trial days and session time.
2. 22. Enter the license key (XXXXX-XXXXX-XXXXX-XXXXX).
3. 33. Activate License (needs internet).
4. 44. Check Now: check the license online now.

Trial

• The trial has every feature for 30 days, without registration.
• During the trial, the gateway bridges data in sessions of 15 minutes. When a session ends, the IEC servers and Modbus polling stop; the dashboard keeps working.
• A new session starts only when the service restarts: Windows Restart-Service MaxIECGateway (administrator PowerShell) or Services → Max IEC Gateway → Restart; Linux sudo systemctl restart maxiec-gateway. Saving settings does not start a new session.
• When the 30 days are over, bridging stays stopped until you enter a license key.

Buying and activating

1. Buy a license on the pricing page ($150 one-time, lifetime license, lifetime free updates). The key arrives by e-mail.
2. Open License in the dashboard, type the key, optionally a device name, and click Activate License.
3. The status bar turns green: Bridging. No restart is needed.

• A license is for one computer. Activating on a second computer gives: This license is already active on another computer.
• The gateway checks the license online about once a day. Without internet it keeps working for up to 30 days after the last successful check; the License page shows the last online check.
• If the license server says the key is invalid, revoked or used elsewhere, the key is removed and the gateway returns to trial mode.

Moving the license to another computer

1. On the old gateway, open License and click Deactivate License (shown when a license is active). This frees the license on the license server; bridging stops on that computer.
2. On the new computer, activate the key as above.

If the old computer no longer works, release it in the license portal with your key and purchase e-mail (up to 5 times in 30 days), or write to support@maxenergic.com. Lost the key? Request it again on the resend page.

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18. Updates

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• The Dashboard shows a blue banner Update Available! when a new version exists. Or click Check for Updates in Settings → About.
• Download the new installer from the download page (the page lists SHA-256 checksums) and run it over the installed version. Configuration, license and password are kept.
• Linux: unpack the new tar.gz and run sudo ./install-linux.sh again.
• Updates are free for life for licensed customers.

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19. Security

The gateway is often installed in an operational network. Use these protections:

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1. 11. HTTP port (default 5000).
2. 22. HTTP only from this computer: other computers must use HTTPS.
3. 33. HTTPS on/off.
4. 44. Certificate file (.pfx) on the gateway computer, and its password.
5. 55. Allowed networks for the dashboard.

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20. Backup and restore

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1. 11. Export Configuration: downloads gateway_config_<date>.json with all devices, mappings and the gateway settings.
2. 22. Choose an exported file to import.
3. 33. Clear existing devices & mappings before import (otherwise the file is added).
4. 44. Also import the IEC/gateway settings from the file.
5. 55. Import Configuration.

• The import checks the whole file first and then applies it in one step: all or nothing.
• Export files of version 1.0 can be imported.
• The dashboard password and the license are not part of the export.

The data folder

Windows: C:\ProgramData\MaxIECGateway (Start menu: Gateway data folder). Linux: /var/lib/maxiec-gateway. To make a full copy, stop the service and copy the whole folder.

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21. Troubleshooting

The log file is in the logs folder of the data folder (Linux: sudo journalctl -u maxiec-gateway). Send it with your question to support@maxenergic.com.

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22. Frequently asked questions

Do I need to restart the gateway after changing a setting?

No. Every change applies immediately. Only the part that is affected restarts, see chapter 15.

Can several SCADA masters connect at the same time?

Yes, up to the Max Connections setting (default 10). Each master receives all data and can send commands.

Can IEC 104 and IEC 101 run at the same time?

Yes. Both serve the same points.

Does it support Modbus RTU?

Yes: Modbus RTU on a serial port (several devices per line) and Modbus RTU over TCP.

Are Modbus addresses 0-based or 1-based?

0-based. Register 40001 is address 0 with data type HoldingRegister.

Why do I get no energy counters in a general interrogation?

That is correct per IEC 60870-5: integrated totals are read with a counter interrogation (C_CI_NA_1).

Is select-before-operate supported?

Yes. Choose Select Before Execute in Settings → Command Options and set the select timeout (1-60 s).

Does the gateway change the computer clock?

Only if you choose "Also set this computer's clock". By default it only confirms and logs the offset.

What happens when the trial session ends?

The IEC servers and Modbus polling stop. Restart the service for a new 15-minute session, or activate a license.

How many computers can use one license?

One. You can move it to another computer at any time.

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Appendix A. Supported ASDU types

Monitor direction (gateway → master):

Control direction (master → gateway):

Not supported: the regulating step command C_RC_NA_1 (47) and the reset process command C_RP_NA_1 (105) get a negative confirmation. Parameter (P_*), file transfer and protection-equipment types are answered with COT 44 (unknown type).

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Appendix B. Cause of transmission (COT) codes

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Appendix C. appsettings.json reference

Most settings are made in the dashboard. A few start-up options are in appsettings.json in the program folder (Windows: C:\Program Files\Max IEC Gateway, Linux: /opt/maxiec-gateway). Edit it with administrator rights and restart the service. The installer keeps your file on updates.

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Appendix D. Service and command-line reference

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Appendix E. Glossary

ACT_CON / ACT_TERM

Activation confirmation (COT 7) and activation termination (COT 10): the outstation's answers to a command.

APCI

The IEC 104 frame header with sequence numbers; controlled by k, w and t0-t3.

ASDU

Application service data unit: one IEC message with type, cause, common address and objects.

Byte order

The order of the bytes of a 32/64-bit value in Modbus registers (ABCD, CDAB, BADC, DCBA).

CA (common address)

Station address in an ASDU; usually 1.

COT

Cause of transmission: why a message is sent (spontaneous, interrogation, activation …).

CP56Time2a

7-byte time tag with date and time to the millisecond (types 30-37).

Deadband

Minimum change before a measured value is sent again.

Double point

A position with two bits: OFF, ON, intermediate or faulty.

General interrogation (GI)

Request from the master for all current values (C_IC_NA_1, QOI 20).

Integrated totals

Counters such as energy (M_IT_*), read by counter interrogation.

IOA

Information object address: number of a data point.

IV / OV

Quality bits: invalid, overflow.

Master / outstation

The SCADA side (controlling station) and the gateway (controlled station).

Modbus RTU / TCP

Modbus on a serial line (RTU) or over Ethernet (TCP).

Select-before-operate (SBO)

Two-step command: select, then execute within the select timeout.

STARTDT / STOPDT

IEC 104 messages that start and stop data transfer on a connection.

Unit ID

Modbus slave address.

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