# EL 4.0 Modbus TCP Communication Interface

# Introduction

Refer to the Reference section for details of the Modbus protocol.

This document describes public Modbus TCP implementation for Enapter Electrolyser EL 4.0 and assume understanding of TCP/IP and Modbus protocols.

# Physical Interface Connection

Connect Ethernet cable to the Ethernet Port of Enapter Electrolyser EL 4.0.

# TCP/IP Connection Settings

By default DHCP client is enabled therefore IP address will be assigned automatically by DHCP server available in the connected network.

It is recommended to set DHCP reservation based on MAC address of the electrolyser.

Configuration of the Static IP is possible using Enapter Cloud and Enapter Mobile Application for iOS and Android.

# Modbus Connection Settings

Option Value Comment
Modbus Port 502
Modbus Slave Address 1 Enapter Electrolyser always addressed as a slave

# References

http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b.pdf (opens new window)

# Data Formats Used

Primary tables Object Type Permission Comment
Input Registers 16 bit word Read Only
Holding Registers 16 bit word Read / Write

# Data Bits/Registers Dimension

Data Type Size in Bits Registers Used Comment
Boolean 16 bits 1 register 0 value means 'false', all other cases - 'true'
Uint16 16 bits 1 register
Uint32 32 bits 2 registers
Uint64 64 bits 4 registers
Float32 32 bits:
* bit 31: Sign (1 bit)
* bit 30-23: Exponent (8 bits)
* bit 22-0: Fraction (23 bits)
2 registers IEEE 754 Single-precision floating-point

# Data Encoding

Big-endian, high word first data encoding used.

This means that when more than single byte (8 bits) is transmitted, network byte order is used - the most significant byte placed at lower address (sent first).

# Implemented Modbus Functions

Function Code Comment
Read Holding Registers 03
Read Input Registers 04
Write Single Holding Register 06
Write Multiple Holding Registers 16

# Modbus Data Model

Input registers and Holding registers are referred to in the range 3XXXX and 4XXXX respectful (also known as PLC Address). For example, Holding register 0 in this document would be referred to as 40001 and would be addressed as register 0000 in the data address field of the Modbus message (also known as Protocol Address).

# Set/Read Modbus IP

To set Modbus IP:

  1. Open the Cloud and navigate to your site
  2. Select EL 4.0 you want to set Modbus IP
  3. Click the Configuration menu item
  4. Click Set Modbus IP
  5. Enter the IP address and then click Create Command
  6. Wait until command will be accepted

To read Modbus IP:

  1. Open the Cloud and navigate to your site
  2. Select EL 4.0 you want to read Modbus IP
  3. Click the Configuration menu item
  4. Click Read Modbus IP
  5. You can see Modbus IP in Execution Payload section

# Modbus Table

# Holding Registers (Read / Write)

Register Data Type Name Comment
0 Uint64 Unix Time Seconds from 1 January 1970 UTC.
e.g. 02/29/2020 @ 3:15 PM (UTC) represented as 1582989315.
4 Boolean Reboot 1 = Reboot.
5 Boolean Locate Electrolyser 1 = Start Blinking All LED; 0 = Stop Blinking All LED.
1000 Boolean Start / Stop Electrolyser 1 = Start; 0 = Stop.
1002 Float32 Production Rate [%] Current production rate in percent (system reset set this value to 'Default Production Rate'), can be changed 'on-fly' even when electrolyser produce H2
1010 Boolean Request Blowdown routine 1 = Request blowdown or read 'is blowdown requested'
1011 Boolean Force Water Refilling 1 = Start Force Water Refilling
1013 Boolean Maintenance Mode 1 = Enable Maintenance Mode; 0 = Disable Maintenance Mode.
1014 Boolean Preheat 1 = Start Preheat
1015 Boolean Flushing Write: 0 = Start Flushing; Read = Flushing state
1016 Boolean Start SIF Proof-Tests 1 = Start
4000 Boolean Configuration Begin 1 = Start configuration
4001 Boolean Configuration Commit 1 = Commit current changes; 0 = Rollback changes
4020 Uint32 Set Ethernet IP Address e.g. 0xC0A80201 (192.168.2.1); 0 = DHCP enabled
4022 Uint32 Set Ethernet IP Netmask Ex: 255.255.255.0
4024 Uint32 Set Ethernet Gateway IP Address Ex: 192.168.2.1
4026 Uint64 Enapter Chassis Serial Number Ex: AA2101019SPI
4038 Uint32 Cloud logs 0 = disable logging (default); 1 = only fatal errors; 2 = fatal errors and errors; 3 = warnings and more important; 4 = everything before and important messages; 5 = all messages, except internal debug ones; 6 = all messages
4042 Uint32 System logs 0 = disable logging (default); 1 = only fatal errors; 2 = fatal errors and errors; 3 = warnings and more important; 4 = everything before and important messages; 5 = all messages, except internal debug ones; 6 = all messages
4044 Uint32 Syslog IP Address Default IP address 255.255.255.255 (Broadcast)
4046 Uint16 Syslog Port Default port 514
4142 Float32 Chassis Altitude [m]
4308 Float32 Set Max Tank Pressure (Outlet) [bar]
4310 Float32 Set Restart Pressure (Outlet) [bar]
4376 Uint64 Enapter Stack Serial Number Ex: 23E21011PI
4396 Float32 Set Default Production Rate [%] This register can be modified only when stack is inactive (Idle or Maintenance mode)
4600 Uint32 Heartbeat ModBus Timeout [Seconds]; 0 = disable
4602 Uint32 Heartbeat Gateway Timeout [Seconds]; 0 = disable
4604 Uint32 Heartbeat UCM Timeout [Seconds]; 0 = disable
4900 Uint32 Period for warmup water level [Milliseconds]
4910 Float32 Minimal Stack current for check [Amperes]
4912 Float32 Threshold for Stack current check [Amperes]
4914 Uint32 Period for Stack current check [Milliseconds]
4916 Uint32 Check Membrane Period [bar]
4926 Uint32 Check Membrane Pressure Threshold [Milliseconds]
4928 Uint32 Check Membrane Voltage Threshold [Volts]
6000 Uint16 Dryer Error Read Dryer error code (bitmask)
6001 Uint16 Dryer Warning Read Dryer warning code (bitmask)
6002 Float32 Dryer TT00 Read temperature of heater element for cartridge 0 (first line)
6004 Float32 Dryer TT01 Read temperature of heater element for cartridge 1 (second line)
6006 Float32 Dryer TT02 Read temperature of heater element for cartridge 2 (first line)
6008 Float32 Dryer TT03 Read temperature of heater element for cartridge 3 (second line)
6010 Float32 Dryer PT00 Read Dryer Input pressure
6012 Float32 Dryer PT01 Read Dryer Output pressure
6014 Float32 PT01 minimal threshold Dryer output pressure at which it leaves Stand-by. Updated value is saved only after writing 1 to register #6022.
6016 Float32 PT01 maximal threshold Dryer output pressure at which it moves to Stand-by. Updated value is saved only after writing 1 to register #6022.
6018 Boolean Start/Stop Dryer Write: 1 = Start; 0 = Stop. Read register #6021 to check Dryer Logic States. Avoid frequent write operations, since it can damage Dryer's Flash.
6019 Uint16 Stop Dryer DEPRECATED
6020 Uint16 Reboot Dryer Write: 1 = Reboot Dryer; Read = number of times Dryer was rebooted. Avoid frequent write operations, since it can damage Dryer's Flash.
6021 Uint16 Dryer state Read Dryer Logic States
6022 Uint16 Save updated Dryer configuration Write: 1 = Save updated Dryer configuration on flash. Avoid frequent write operations, since it can damage Dryer's Flash.
6023 Uint16 Locate Dryer in DCN/IDCN 0 = Disable; 1 = Enable
6024 Uint16 Reboot UCM Write: 1 = reboot UCM
6200 Uint32 Water Tank status Read Water Tank States (bitmask)
6202 Float32 Water Tank water level [Liters]
6204 Float32 Water Tank inlet temperature [ยฐC]
6206 Float32 Water Tank tank temperature [ยฐC]
6208 Float32 Water Tank conductivity [ฮผS/cm]
6210 Float32 Water Tank pump current [Amperes]
6220 Uint32 Water Tank UCM uptime [Seconds]
6222 Uint16 Command to Water Tank Write: 1 = Start; 2 = Stop; 3 = Reboot WT control board; 4 = Reboot WT UCM board; 5 = Locate OFF; 6 = Locate ON; 7 = Maintenance OFF; 8 = Maintenance ON
7000 Boolean Electrolyte Heater (H102) condition 0 = Disable; 1 = Enable
7005 Boolean Cooling valve V106 0 = Close; 1 = Open
7007 Boolean Recombiner Heater (H109) condition 0 = Disable; 1 = Enable

# Input Registers (Read Only)

Register Data Type Name Comment
0 Uint32 Device Model 0x45343031U ("EL40")
2 Uint16 Firmware MAJOR and MINOR Version Ex: 0x0100 (1.0)
3 Uint16 Firmware PATCH Version Ex: 0x0011 (17)
4 Uint32 Firmware Build Number Ex: 0x4E343471
6 Uint128 Device Control Board Serial Number Ex: 9E25E695-A66A-61DD-6570-50DB4E73652D
14 Uint64 Chassis Serial Number 1 bits - reserved, must be 0
10 bits - Product Unicode
11 bits - Year + Month
5 bits - Day
24 bits - Chassis Number
5 bits - Order
8 bits - Site
Example
18 Uint16 System State 0 = Internal Error, System not Initialized yet; 1 = System in Operation; 2 = Error; 3 = System in Maintenance Mode; 4 = Fatal Error; 5 = System in Expert Mode.
20 Uint32 Live time [seconds] Total time during which a system is power up (not only time when stack is working).
22 Uint32 Uptime [seconds] How long the system has been running
26 Uint32 Free memory Memory which can be used
28 Uint32 Available memory Memory which has not been allocated yet
30 Uint32 Free space on flash-card Space on flash-card where the configuration is
768 Array of 32 Warning Events Warning Events Array Warning Events Array represented by Error Codes. First Uint16 contains total quantity of Warning Events.
832 Array of 32 Error Events Error Events Array Error Events Array represented by Error Codes. First Uint16 contains total quantity of Error Events.
1000 Uint32 Stack Serial Number 1 bits - reserved, must be 0
15 bits - Stack Type
11 bits - Year + Month
29 bits - Stack Number
8 bits - Site
1002 Uint32 Stack Start/Stop Cycles Quantity How many Stack Start/Stop cycles
1004 Uint32 Stack Total Runtime seconds
1006 Float32 Stack Total H2 Production NL
1008 Float32 H2 Flow Rate NL/hour, NAN when not producing H2;
1010 Uint64 Product Code 28 = ELE400535A2ASV01
29 = ELE400535D4ASV01
2A = ELE400535A2LSV01
2B = ELE400535D4LSV01
1200 Uint16 Electrolyser State 0 = Halted; 1 = Maintenance mode; 2 = Idle; 3 = Steady; 4 = Stand-By (Max Pressure); 5 = Curve; 6 = Blowdown; 7 = Recombiner.
4000 Boolean Configuration Progress 1 = Configuration is in progress.
4001 Boolean Configuration Source 1 = Configuration over Modbus.
4002 Int32 Last Configuration Result 0 = OK, Configuration was completed successfully; 1 = Permanent, The operation has failed (internal or general error); 2 = No Entry, Configuration was not started or interrupted; 5 = I/O, Data save error; 11 - Try again, Configuration needs to be tried again; 13 = Access Denied, Some changed registers are read-only; 16 = Busy, Another configuration was in progress; 22 = Invalid, The data has invalid or wrong type.
4004 Uint16 Last Configuration Wrong Holding Keeps first invalid Holding register number which doesn't allow successful configuration commit.
4600 Uint16 Heartbeat Timeout for Modbus Heartbeat in seconds. 0 = disabled (default)
4417 Boolean Flushing done 1 = Done
4418 Int32 Mixing time after tank is filled with water [ms]
6000 Uint16 Dryer Error Dryer error code (bitmask).
6001 Uint16 Dryer Warning Dryer warning code (bitmask).
6002 Float32 Dryer TT00 Temperature of heater element for cartridge 0 (first line).
6004 Float32 Dryer TT01 Temperature of heater element for cartridge 1 (second line).
6006 Float32 Dryer TT02 Temperature of heater element for cartridge 2 (first line).
6008 Float32 Dryer TT03 Temperature of heater element for cartridge 3 (second line).
6010 Float32 Dryer PT00 Input pressure of the dryer.
6012 Float32 Dryer PT01 Output pressure of the dryer.
6100 Uint32 3 OUI octets for Wi-Fi MAC address Ex: C8:2B:96
6102 Uint32 3 NIC octets for Wi-Fi MAC address Ex: A8:F5:2C
6104 Boolean Dryer Control Network Connection Status 1 = Online; 0 = Offline
7000 Boolean High Electrolyte Level Switch (LSH102B_in) 1 = Electrolyte level over sensor; 0 = Electrolyte level below sensor.
7001 Boolean Very High Electrolyte Level Switch (LSHH102A_in) 1 = Electrolyte level over sensor; 0 = Electrolyte level below sensor.
7002 Boolean Low Electrolyte Level Switch (LSL102D_in) 1 = Electrolyte level over sensor; 0 = Electrolyte level below sensor.
7003 Boolean Medium Electrolyte Level Switch (LSM102C_in) 1 = Electrolyte level over sensor; 0 = Electrolyte level below sensor.
7004 Boolean Electrolyte Tank High Pressure Switch (PSH102_in) 1 = Pressure is too high; 0 = Pressure is normal.
7007 Boolean Electronic Compartment High Temperature Switch (TSH108_in) 1 = Temperature is too high. 0 = Temperature is normal.
7009 Boolean Chassis Water Presence Switch (WPS104_in) 1 = Water is present on input; 0 = No water input.
7010 Boolean Dry Contact 1 = OK (Closed); 0 = NOT OK (Opened)
7500 Float32 Electrolyte Cooler Fan Speed (F103A_in_rpm) [rpm]
7502 Float32 Air Circulation Fan Speed (F104B_in_rpm) [rpm]
7504 Float32 Electronic Compartment Cooling Fan Speed (F108C_in_rpm) [rpm]
7506 Float32 Electrolyte Flow Meter (FM106_in_lmin) [Liters per minute]
7508 Float32 Stack Current (HASS_in_a) [Ampere]
7510 Float32 PSU Voltage (Stack Voltage) (PSU_in_v) [Volt]
7512 Float32 Inner Hydrogen Pressure (PT101A_in_bar) [bar]
7514 Float32 Outer Hydrogen Pressure (PT101C_in_bar) [bar]
7516 Float32 Water Inlet Pressure (PT105_in_bar) [bar]
7518 Float32 Electrolyte Temperature (TT102A_in_c) [ยฐC]
7520 Float32 Downstream Temperature (TT106_in_c) [ยฐC]
8002 Float32 Outer Hydrogen Pressure Raw Sensor Value (PT101C_in_v) Raw value, [Volt]
8004 Float32 Stack Current Raw Sensor Value (HASS_in_v) Raw value, [Volt]

# Dryer error/warning code bitmask

Dryer error/warning code bitmask (opens new window) is 16-bit value where each bit representing one type of error. The following table provides the detailed description of each error.

Bit number Description
0 TT00 has invalid value (sensor provides unexpected values)
1 TT01 has invalid value (sensor provides unexpected values)
2 TT02 has invalid value (sensor provides unexpected values)
3 TT03 has invalid value (sensor provides unexpected values)
4 TT00 value growth is not enough (heating mechanism does not work properly)
5 TT01 value growth is not enough (heating mechanism does not work properly)
6 TT02 value growth is not enough (heating mechanism does not work properly)
7 TT03 value growth is not enough (heating mechanism does not work properly)
8 PS00 (pressure switch on line 0) is triggered
9 PS01 (pressure switch on line 1) is triggered
10 F100 has invalid RPM speed (fan between line 0 and line 1)
11 F101 has invalid RPM speed (fan on line 0)
12 F102 has invalid RPM speed (fan on line 1)
13 PT00 (Input pressure) has invalid value (sensor provides unexpected values)
14 PT01 (Output pressure) has invalid value (sensor provides unexpected values)

# Water Tank States (bitmask)

Water Tank status bitmask (opens new window) is 32-bit value where bit representing one type of status. The following table provides the detailed description of each state.

Bit number State Name
0 N/A
1 Stop
2 Maintenance
4 Bad quality water input
5 Waiting for water
6 High water inlet temperature
7 Low water inlet temperature
8 Very low water level
9 Low water level
10 Very high water level (warning)
12 Low water tank temperature
14 Very high water level (fatal error)
15 Tank refilling issue
16 Tank temperature sensor broken
17 Inlet temperature sensor broken
18 Water level sensor broken
20 Current sensor broken
21 Water leak
22 Valve leak
23 Pump broken
25 Factory settings reset failed
26 Internal error

# Diagrams

# System State Diagram

This diagram describes possible transition between different electrolyser states. The state can be read in the Input Register #18.

# Examples

# Example: Reading Chassis Serial Number

Read from Modbus 586601960808264448.

Decode into binary format 0001000001 00100000001 11011 000000001101010000110001 10011 00000000 and parse every part.

Product Unicode = 0b0001000001 = 65 : 2 (A=1, B=2,..., Z=26 => 'B') * 32 + 1 (=>'A') => 'AB'

Year + Month = 0b00100000001 = 257 : 21 * 12 + 5 => May 2021

Day = 0b11011 = 27

Chassis Number = 0b000000001101010000110001 = 54321

Order = 0b10011 = 19: (=>S)

Site = 0b000000 = 0 (0 - PIsa, 1 - SAerbeck => PI)

Result Chassis Serial Number - AB 21 05 27 54321 S PI

# Example: Change Electrolyser Restart Pressure over Modbus TCP

Here is an example to change Electrolyser Restart Pressure to 25 bar over Modbus TCP. This will enable Electrolyser to restart when pressure drop to 25 bar on outlet.

# Example: Reading Modbus Input Registers

  • Request Packet

    Transaction ID Protocol ID Query Length Unit ID Function Code Reference Number Word Count
    00 01 00 00 00 06 01 04 03 EE 00 02
  • Request Packet Description

    Modbus/TCP

    • Transaction ID โ€“ default: 00 01
    • Protocol ID โ€“ default: 00 00
    • Query Length โ€“ default: 00 06
    • Unit ID: Slave Address โ€“ default: 01

    Modbus

    • Function Code: Read Input Registers โ€“ default: 04
    • Reference Number: Starting register โ€“ decimal: 1006
    • Word Count: Number of registers to read โ€“ decimal: 2
  • Wireshark Example

    Reading Modbus Request

  • Response Packet

    Transaction ID Protocol ID Query Length Unit ID Function Code Byte Count Register[0] Register[1]
    00 01 00 00 00 07 01 04 04 48 00 10 7A
  • Response Packet Description

    Modbus/TCP

    • Transaction ID โ€“ default: 00 01
    • Protocol ID โ€“ default: 00 00
    • Query Length โ€“ decimal: 7
    • Unit ID: Slave Address โ€“ default: 01

    Modbus

    • Function Code: Read Input Registers โ€“ default: 04
    • Byte Count: Registers values size โ€“ decimal: 4
    • Register[0] value โ€“ decimal: 18432
    • Register[1] value โ€“ decimal: 4218
    • Register[โ€ฆ] value โ€“ 2 bytes
  • Wireshark Example

    Reading Modbus Response

# Example: Writing to Modbus Holding Registers

  • Request Packet

    Transaction ID Protocol ID Query Length Unit ID Function Code Reference Number Data
    00 01 00 00 00 06 01 06 00 04 00 01
  • Request Packet Description

    Modbus/TCP

    • Transaction ID โ€“ default: 00 01
    • Protocol ID โ€“ default: 00 00
    • Query Length โ€“ default: 00 06
    • Unit ID: Slave Address โ€“ default: 01

    Modbus

    • Function Code: Write Single Register โ€“ default: 06
    • Reference Number: Starting register โ€“ decimal: 4
    • Data: Value to write โ€“ decimal: 1
  • Wireshark Example

    Writing Modbus Request

  • Response Packet

    Transaction ID Protocol ID Query Length Unit ID Function Code Reference Number Data
    00 01 00 00 00 06 01 06 00 04 01
  • Response Packet Description

    Modbus/TCP

    • Transaction ID โ€“ default: 00 01
    • Protocol ID โ€“ default: 00 00
    • Query Length โ€“ default: 00 06
    • Unit ID: Slave Address โ€“ default: 01

    Modbus

    • Function Code: Write Single Register โ€“ default: 06
    • Reference Number: Register to write โ€“ decimal: 4
    • Data: Value to write โ€“ decimal: 1
  • Wireshark Example

    Writing Modbus Response

# Example: Reading Errors Sequence

  • Request Packet

    Transaction ID Protocol ID Query Length Unit ID Function Code Reference Number Word Count
    00 01 00 00 00 06 01 04 03 40 00 20
  • Request packet description

    Modbus/TCP

    • Transaction ID โ€“ default: 00 01
    • Protocol Identifier โ€“ default: 00 00
    • Query Length โ€“ default: 00 06
    • Unit ID: Slave Address โ€“ default: 01

    Modbus

    • Function Code: Read Input Registers โ€“ default: 04
    • Reference Number: Starting register โ€“ default: 03 40
    • Word Count: Number of registers to read โ€“ default: 00 20
  • Wireshark Example

    Reading Errors Request

  • Response Packet

    Transaction ID Protocol ID Query Length Unit ID Function Code Byte Count Register[0] Register[1]
    00 01 00 00 00 43 01 04 40 00 01 11 B3
  • Response packet description

    Modbus/TCP

    • Transaction ID โ€“ default: 00 01
    • Protocol ID โ€“ default: 00 00
    • Query Length โ€“ default: 00 43
    • Unit ID: Slave Address โ€“ default: 01

    Modbus

    • Function Code: Read Input Registers โ€“ default: 04
    • Byte count: Registers values size โ€“ default: 40
    • Register[0] value โ€“ total number of errors, decimal: 1
    • Register[1] value โ€“ error code 1: 11 B3
    • Register[โ€ฆ] value โ€“ error code N
  • Wireshark Example

    Reading Errors Response

# Example: Writing Heartbeat Modbus Timeout

  • Request Packet

    Transaction ID Protocol ID Query Length Unit ID Function Code Reference Number Data
    00 02 00 00 00 06 01 06 0F A0 00 01
  • Request Packet Description

    Modbus/TCP

    • Transaction ID โ€“ decimal: 2
    • Protocol ID โ€“ default: 00 00
    • Query Length โ€“ default: 00 06
    • Unit ID: Slave Address โ€“ default: 01

    Modbus

    • Function Code: Write Single Register โ€“ default: 06
    • Reference Number: Starting register โ€“ decimal: 4000
    • Data: Value to write โ€“ decimal: 1
  • Wireshark Example

    Writing Heartbeat Modbus Timeout Request 1

  • Response Packet

    Transaction ID Protocol ID Query Length Unit ID Function Code Reference Number Data
    00 02 00 00 00 06 01 06 0F A0 00 01
  • Response Packet Description

    Modbus/TCP

    • Transaction ID โ€“ decimal: 2
    • Protocol ID โ€“ default: 00 00
    • Query Length โ€“ default: 00 06
    • Unit ID: Slave Address โ€“ default: 01

    Modbus

    • Function Code: Write Single Register โ€“ default: 06
    • Reference Number: Register to write โ€“ decimal: 4000
    • Data: Value to write โ€“ decimal: 1
  • Wireshark Example

    Writing Heartbeat Modbus Timeout Response 1

  • Request Packet

    Transaction ID Protocol ID Query Length Unit ID Function Code Reference Number Data
    00 03 00 00 00 06 01 06 11 F8 00 00
  • Request Packet Description

    Modbus/TCP

    • Transaction ID โ€“ decimal: 3
    • Protocol ID โ€“ default: 00 00
    • Query Length โ€“ default: 00 06
    • Unit ID: Slave Address โ€“ default: 01

    Modbus

    • Function Code: Write Single Register โ€“ default: 06
    • Reference Number: Starting register โ€“ decimal: 4600
    • Data: Value to write โ€“ decimal: 0
  • Wireshark Example

    Writing Heartbeat Modbus Timeout Request 2

  • Response Packet

    Transaction ID Protocol ID Query Length Unit ID Function Code Reference Number Data
    00 03 00 00 00 06 01 06 11 F8 00 00
  • Response Packet Description

    Modbus/TCP

    • Transaction ID โ€“ decimal: 3
    • Protocol ID โ€“ default: 00 00
    • Query Length โ€“ default: 00 06
    • Unit ID: Slave Address โ€“ default: 01

    Modbus

    • Function Code: Write Single Register โ€“ default: 06
    • Reference Number: Register to write โ€“ decimal: 4600
    • Data: Value to write โ€“ decimal: 0
  • Wireshark Example

    Writing Heartbeat Modbus Timeout Response 2

  • Request Packet

    Transaction ID Protocol ID Query Length Unit ID Function Code Reference Number Data
    00 04 00 00 00 06 01 06 0F A1 00 01
  • Request Packet Description

    Modbus/TCP

    • Transaction ID โ€“ decimal: 4
    • Protocol ID โ€“ default: 00 00
    • Query Length โ€“ default: 00 06
    • Unit ID: Slave Address โ€“ default: 01

    Modbus

    • Function Code: Write Single Register โ€“ default: 06
    • Reference Number: Starting register โ€“ decimal: 4001
    • Data: Value to write โ€“ decimal: 1
  • Wireshark Example

    Writing Heartbeat Modbus Timeout Request 3

  • Response Packet

    Transaction ID Protocol ID Query Length Unit ID Function Code Reference Number Data
    00 04 00 00 00 06 01 06 0F A1 00 01
  • Response Packet Description

    Modbus/TCP

    • Transaction ID โ€“ decimal: 4
    • Protocol ID โ€“ default: 00 00
    • Query Length โ€“ default: 00 06
    • Unit ID: Slave Address โ€“ default: 01

    Modbus

    • Function Code: Write Single Register โ€“ default: 06
    • Reference Number: Register to write โ€“ decimal: 4001
    • Data: Value to write โ€“ decimal: 1