Modbus RTU installation for DEIF SGC 120 / SGC 121

  • Updated on Sep 30, 2026
  • Published on Sep 30, 2026
  • 5 minute(s) read
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This article explains the process of configuring Modbus RTU and implementing a RS-485 connection to a Calculus C06 gateway.

Objective

A technician must be able to place the SGC 120 / SGC 121 safely in configuration mode, set the correct Modbus parameters, and connect the RS-485 wiring correctly to the C06.

Scope

This guide covers the DEIF SGC 120, SGC 120 Mk II and SGC 121 for Modbus RTU configuration and the physical RS-485 connection to a Calculus C06. Configuration of the Calculus gateway in the platform is outside the scope of this document.

Compatibility

The Modbus RTU wiring and settings in this guide apply to SGC 120, SGC 120 Mk II and SGC 121. Menu labels can differ slightly by model or firmware. SGC 110 is not covered because it does not provide the RS-485 port used in this procedure.

1. Safety first

Warning

Make sure the generator cannot start unexpectedly. Put the controller in MANUAL and de-energise wiring work where required. Follow the safety procedures of the generator manufacturer/OEM.

  • If the controller is in AUTO mode, press STOP to return to MANUAL.

  • Disconnect the RS-485 connector before installing or changing the communication wiring.

  • Do not touch mains, generator or power terminals while carrying out these steps.

2. Standard Modbus settings

Use the settings below for Calculus installations on the SGC 120 / SGC 121.

Parameter

Value

Protocol

Modbus RTU

Server/Slave ID

1

Baud rate

9600 bps

Data bits

8

Parity

None

Stop bit

1

Serial format

9600 / 8N1

Depending on the controller version, the display may show Server ID or Modbus Slave ID. For Calculus, set the address to 1. The communication format used is 9600 / 8N1.

3. Buttons on the SGC 120 / SGC 121

4. Configure Modbus on the DEIF SGC 120 / SGC 121

Follow the steps below on the controller. Do not change generator, protection or application parameters that are not mentioned in this procedure.

  1. Put the controller in MANUAL
    If the controller is in AUTO mode, press STOP to return to MANUAL.

  2. Open Configuration mode
    Hold STOP / CONFIG for at least 3 seconds.

  3. Press START to continue
    This opens the configuration / write mode so parameters can be changed.

  4. Enter the password
    Use 0123 for Level 1 / full read-write access. Use ▲ and ▼ to select a digit and START to confirm.

If 0123 does not work

The factory password may have been changed by the generator manufacturer/OEM. Use the known OEM password or contact the responsible party - do not reset or change unrelated settings to force access.

  1. Open the communication settings
    On SGC 120 Mk II use Module → Communication. On SGC 120 / SGC 121 use the RS485 COMM / Communication menu. Set only the parameters shown below.

Menu parameter

Setting

Communication Mode / COMM MODE

Modbus

Server ID / MODBUS SLAVE ID

1

Baud rate / BAUDRATE

9600

Parity Bit / PARITY

None

  1. Save and exit Configuration mode
    Hold STOP / CONFIG to return to MANUAL. Wait until saving has completed.

Result

The DEIF controller is now ready for Modbus RTU communication with address 1 and communication format 9600 / 8N1.

5. Connect RS-485 to the Calculus C06

The SGC 120 and SGC 121 use a 2-wire, half-duplex RS-485 port. The relevant connections are terminal 16 (A) and terminal 15 (B).

SGC 120 / 121

Function

C06

Wire

Terminal 16

RS-485 A

C06 A+ / Data+

Brown

Terminal 15

RS-485 B

C06 B- / Data-

White

No separate RS-485 GND

-

C06 GND

Green (normally not connected)

Important

Do not connect the green C06 GND wire to DEIF terminal 1 for this point-to-point connection. Terminal 1 is the power ground - the Modbus port itself is documented on terminals 15 and 16.

Termination

The SGC 120 / SGC 121 documentation specifies termination on the RS-485 port. For SGC 120 Mk II or non-standard bus topologies, verify the actual controller and DEIF wiring documentation before adding any additional 120 ohm resistor.

6. Cabling

  • Use a suitable RS-485 cable with a twisted pair for Data+ and Data-.

  • Keep the data cable away from power cables, contactors, starter motor wiring and other sources of electrical interference.

  • Use the cable shield according to the installation standard; normally connect the shield to earth at one side only.

  • Make sure the conductors are firmly secured and that no loose copper strands can cause a short circuit.

  • For termination, follow the DEIF documentation for the installed controller version and bus topology. Do not add an extra 120 ohm resistor by default without checking the existing termination.

Note on A/B labels

A/B, +/-, and Data+/Data- are not labelled consistently by all manufacturers. For this installation, use: DEIF terminal 16 (A) to C06 A+ / Data+, and terminal 15 (B) to C06 B- / Data-.

7. Check after installation

  1. Visual check Terminal 16 runs to C06 A+ and terminal 15 to C06 B-. No loose or damaged conductors.

  2. Check settings Communication Mode = Modbus, ID = 1, Baud rate = 9600, Parity = None.

  3. Exit configuration The controller has left Configuration mode and is back in the required operating mode.

  4. Connect the gateway Reinstall the C06 RS-485 connector and power the installation according to the applicable procedure.

  5. Check communication During commissioning, verify that valid Modbus data is received from the DEIF controller.

8. Troubleshooting

Problem

Possible cause

Check / action

No communication

A/B swapped or wired incorrectly

Check 16 → A+ (brown) and 15 → B- (white).

No communication

Serial settings do not match

Check ID 1, 9600 baud, 8 data bits, parity None, 1 stop bit.

Cannot enter configuration

Controller not in MANUAL

Press STOP to select MANUAL, then hold STOP / CONFIG for at least 3 seconds.

Password 0123 does not work

OEM changed the password

Use the known OEM password or request it from the generator manufacturer.

Intermittent communication

Interference or poor wiring

Check twisted pair, cable routing, connections and shielding.

Connector appears reversed

Viewing direction of the loose C06 connector

Follow function and wire colour, not only left/right position.

9. Quick reference for the technician

SGC 120 / SGC 121 Modbus

MANUAL → STOP / CONFIG (≥ 3 s.) → START → password 0123 → Communication → Modbus → ID 1 → Baud rate 9600 → Parity None → save and exit

Settings

  • Protocol: Modbus RTU

  • Server / Slave ID: 1

  • Baud rate: 9600

  • Parity: None

  • Frame: 8N1

Connection

  • DEIF 16 (A) → C06 A+ / Data+ (brown)

  • DEIF 15 (B) → C06 B- / Data- (white)

  • C06 GND (green) → normally not connected

  • Check termination before adding an extra 120 ohm resistor

Final check

  • Controller safe and in the correct operating mode

  • Modbus settings correct

  • A/B wiring correct

  • Connector firmly installed

  • Communication confirmed during commissioning

Sources and technical verification

  • DEIF - Documentation for SGC 120

  • DEIF - Documentation for SGC 121

  • DEIF - SGC 120 Mk II User Manual and online documentation

  • DEIF - SGC 120/121 User Manual 4189341226C; Calculus - RS-485 / Modbus RTU connection; Calculus - Installing C06 in a generator

Technical values checked on 21/09/2026. If the controller firmware or OEM configuration differs, always verify against the current DEIF documentation.

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