Modbus
Modbus Protocol
Description
The powerIO box T1.B100 is used as a gateway between Modbus TCP and Modbus RTU. The configuration of the serial ports for Modbus RTU can be performed flexibly.
The Unit ID of the Modbus device to be addressed must be specified by the Modbus client (typically a controller). Through an automatic scan, the Modbus devices are assigned to the corresponding serial ports. This assignment is stored in an internal list.
Special features:
Behavior with unavailable devices For unavailable devices, no blocking timeouts are generated, allowing communication with other participants to continue uninterrupted.
Testing of connected devices The connected devices can be tested and checked autonomously via an internal Modbus test without a previously completed Modbus-TCP client logic.
Modbus trace log for error analysis For error analysis, a Modbus trace log is provided. This records queries from all Modbus-TCP clients. Performance values are also provided.
Support for multi-master queries Queries from multiple Modbus-TCP clients can be performed in parallel. The queries are processed in a queue and assigned to the corresponding Modbus-TCP client.
Selection for Modbus protocol
Modbus is always selected as the default for a serial port. However, if another protocol was previously selected, Modbus mode can be chosen via the "Fieldbus" dropdown menu.
Modbus Test
A complete Modbus test client is implemented on the powerIO box T1.B100. This works even if it is accessed by another existing Modbus TCP client.
Supported function codes of the Modbus test
Read:
FC 1 - Read Coil Status
FC 2 - Read Input Status
FC 3 - Read Holding Register
FC 4 - Read Input Register
Write:
FC 5 - Write Coil
FC 6 - Write Register
FC 15 - Write Multiple Coil
FC 16 - Write Multiple Register
Further functions
Representation for different data types: boolean, byte, sbyte, uint16, int16, uint32, int32, float32, uint64, int64, float64, double, string
Byte swapping
Little and big endian
Modbus log
The Modbus trace log enables monitoring and analyzing Modbus communication data in real time. Filters can be used to display specific data, and the log data can be exported for further analysis.
Enabling/disabling the Modbus log:
Modbus logging is disabled via the "DISABLE MODBUS LOG"button.
The timer at the top right indicates the remaining time before logging is automatically disabled.
Filter options: Various filter options are provided for targeted analysis of the log data:
State: Filtering by status (successful/failed).
Unit ID: Narrowing down by a specific device ID.
Type: Serial or internal registers of the Modbus TCP gateway T1.B100
Serial Port: Assigned serial port
Function Code: Filter by function code
Start Address: The register address
Quantity: The number of registers
The displayed logs are adjusted according to the filter selection.
Actions:
RESET FILTER: All filter settings are reset.
CLEAR DATA: The displayed log data is cleared from the interface.
EXPORT DATA: The filtered log data is exported in CSV format for further external processing.
Display of log data
The displayed logs contain the following information:
Timestamp: The timestamp of the Modbus request is shown.
State: The status of the request is displayed (e.g. ✅ for successful).
Info: Details of the request are provided, including:
Unit ID: The Unit ID
Type: Device type (e.g. T1.B100 or Serial with port assignment).
Request Data:
FC (Function Code): The used Modbus command is shown.
Address: The start address of the access is indicated.
Quantity: The number of read registers is displayed.
Response Data:
Read Value: The values returned by the target device are shown (RTU).
Processing Time: The duration of the request processing is given in milliseconds.
Internal registers
The powerIO box T1.B100 has an internal Modbus TCP Unit ID. This Unit ID is 248
Attention: From firmware version v4.0 the Unit ID was changed to 248 In earlier firmware versions (before v4.0) the Unit ID was 240.
This change was made because the Unit ID 240 is a valid serial Unit ID. The value range for serial Unit IDs is between 1 and 247.
FC3 / FC4
1000
20
Hostname
string
1020
20
Box name
string
1040
20
Box comment
string
1060
1
CPU utilization
UINT16 (0.1)
1061
1
RAM utilization
UINT16 (0.1)
1062
6
System time
UINT16
1068
4
Uptime
UINT16
1072
1
CPU temperature
UINT16 (0.1)
1073
1
System temperature 1
UINT16 (0.1)
1074
1
System temperature 2 5V
UINT16 (0.1)
1075
1
System temperature 3 compute module
UINT16 (0.1)
1080
20
Serial number
string
1100
20
System ID1
string
1120
20
System ID2
string
1150
1
Current 24V power supply
UINT16 (0.01)
1151
1
Voltage 24V power supply
UINT16 (0.01)
1152
1
Power 24V power supply
UINT16 (0.01)
1153
1
Voltage 5V power supply
UINT16 (0.01)
1154
1
Voltage 3.3V power supply
UINT16 (0.01)
1155
1
Voltage 3.3V compute module
UINT16 (0.01)
1156
1
Voltage 1.8V compute module
UINT16 (0.01)
1160
1
Fault current 24V power supply
UINT16
1161
1
Fault voltage 24V power supply
UINT16
1162
1
Fault power 24V power supply
UINT16
1163
1
Fault voltage 5V power supply
UINT16
1164
1
Fault voltage 3.3V power supply
UINT16
1165
1
Fault voltage 3.3V compute module
UINT16
1166
1
Fault voltage 1.8V compute module
UINT16
2021
1
Bus port 1 configuration
UINT16
2022
1
Bus port 2 configuration
UINT16
2023
1
Bus port 3 configuration
UINT16
2024
1
Bus port 4 configuration
UINT16
2025
1
Bus port 5 configuration
UINT16
3000
20
Ethernet adapter
string
3020
20
Link
string
3040
20
Mode
string
3060
20
MAC
string
3080
1
Link
UINT16
3081
1
Network mode (number)
UINT16
3090
6
MAC
string
3100
4
IP address
UINT16
3104
4
Subnet mask
UINT16
3108
4
Gateway IP
UINT16
3112
4
DNS1 IP
UINT16
3116
4
DNS2 IP
UINT16
3120
4
Broadcast IP
UINT16
3130
10
IP address
string
3140
10
Subnet mask
string
3150
10
Gateway IP
string
3160
10
DNS1 IP
string
3170
10
DNS2 IP
string
3180
10
Broadcast IP
string
Example - query IP address
Modbus exception codes
Code
Name
Description
01
Illegal Function
The function code is not supported by the slave.
02
Illegal Data Address
The requested address is invalid. The length may be wrong, or it is an invalid register address.
03
Illegal Data Value
A value in the data field of the request is invalid. The structure of the request is faulty, e.g. wrong length or not permitted values.
04
Slave Device Failure
A non-recoverable error occurred during processing.
05
Acknowledge
The request has been accepted, but processing takes longer. The master should query later whether processing is complete.
06
Slave Device Busy
The device is currently busy and cannot execute the request. The master should retry the request later.
07
Negative Acknowledge
The device cannot execute the request, e.g. in case of faulty programming requests.
08
Memory Parity Error
A consistency error was detected in memory. The device can try the request again, but a service may be required.
10 (0A)
Gateway Path Unavailable
This error usually occurs when the TCP query to the gateway is successful, but the device cannot be assigned.
11 (0B)
Gateway Target Device Failed to Respond
This error code occurs when the device is already assigned but no longer responds.
Last updated