MD20002 Modbus RTU 16 Relays (EN)
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Description
16-relay card controlled via RS485 and Modbus RTU
The Modig Modbus 16R module is equipped with 16 SPDT electromagnetic relays, which are controlled using Modbus standard commands transmitted via the RS485 interface. The control interface features galvanic isolation and surge protection, ensuring stable operation even in installations exposed to severe interference. The communication and operational parameters of the module can be flexibly configured and adapted to the requirements of various applications.
Key Features and Parameters
- 16 relay outputs - NC/NO contacts, 10 A, 250 V AC / 30 V DC
- RS485 interface with galvanic isolation and surge protection
- Configurable communication parameters:
- baud rate: 1200…1000000;
- parity: none/even/odd;
- stop bits: 1/1.5/2
- Power supply: 5 V (4.9…5.3 V) with a minimum current capacity of 1.5 A
- Power delivery via USB-C connector, 2.1/5.5 mm DC barrel jack, or Phoenix MC 3.81 mm connector
- Control and configuration of settings via Modbus commands
- Measurement of power supply voltage and module temperature
- Dimensions: 200x110x60 mm
- Mounting on DIN-35 rail
Relay Connectors
The relay contacts are routed to screw terminals with a 5.08 mm pitch. Each of the 16 outputs offers normally closed (NC) and normally open (NO) contacts. When a given output is turned on, the NO contact is connected to the common contact (COM), while the NC contact is disconnected from COM. The active state for a specific output is indicated by a lit LED located near the terminals of that connector. The layout of individual pin assignments is shown in the figure.
An example circuit controlled using the Modig Modbus 16 Relays is shown in the figure.
RS485 Interface
The RS485 interface is brought out as a 4-pin Phoenix Contact MC 3.81 mm connector. Depending on the installation, only lines A+ and B- or all lines T, A+, B-, and G can be used. Their functions are described in the table.
| Designation | Function |
|---|---|
| 120 Ω / T | Activation of the internal 120 Ω termination
resistor. The resistor is active when terminal T is connected to terminal A+, e.g., using a jumper installed directly inside the plug. |
| A+ | Line A of the RS485 bus (positive potential) |
| B- | Line B of the RS485 bus (negative potential) |
| GND / G | Signal ground GND of the RS485 bus. |
The RS485 interface is galvanically isolated from the remaining components and equipped with surge protection elements, ensuring stable operation even in installations exposed to severe interference.
The RS485 communication parameters are configured using Modbus commands; the default settings are: 19200, 8, none, 1.
The Modig Modbus 16R module can be connected to an RS485 bus that links up to 64 devices (including the module). Each device should be connected in a way that prevents bus branching – any stubs should be kept as short as possible. At both ends of the bus, it is recommended to connect 120 Ω termination resistors. Modig Modbus 16R has such a resistor integrated, but to activate it, the A+ and T terminals must be connected together inside the plug.
The figure shows a simplified diagram of the RS485 bus, terminated with a 120 Ω resistor on one end, and with the integrated termination resistor in the module on the other end. Furthermore, correct and incorrect methods of connecting devices to the bus are shown.
Power Supply
The Modig Modbus 16R module is equipped with 3 different power connectors, connected in parallel. Only one of them must be chosen to connect a power supply with a voltage of 4.9…5.3 V, a minimum capacity of 1.5 A, and correct polarity.
| Connector | Function |
|---|---|
| USB-C (J3) | Standard USB-C socket, serves only a power delivery function |
| 2.1/5.5 (J2) | 2.1/5.5 mm DC barrel jack compatible with
"brick-type" power adapters. Note the polarity – center positive. |
| MC 3.81 mm (J1) | Terminal block connector for wire attachment. Note the polarity – positive terminal on the side facing the relays. |
LED Indicators
There are two status LEDs on the Modig Modbus 16R board that inform about the device's operation.
| Indicator | Function |
|---|---|
| STA | A continuously lit LED with brief, cyclic blanking indicates correct operation of the device |
| BUS | A blinking LED indicates data reception from the RS485 bus and Modbus commands |
Factory Reset
There is a SET tactile micro-button on the Modig Modbus 16R module board. Pressing and holding it for approximately 5 seconds will restore all settings (configuration register values) to their defaults. This function is useful in situations where incorrect parameter settings prevent sending Modbus commands to the module. Restoring defaults sets the RS485 communication parameters to: 19200, 8, none, 1 and the module address to "1".
Configuration Registers (Holding Registers)
All parameters of the device are defined by the values of configuration registers, known as Holding Registers. These registers can be read and written using Modbus commands to modify the device's operation. The list of registers and their functions are described in the table.
| Register Number (hex) | Name | Description | Default Value /
Value Range |
|---|---|---|---|
| x4000 | Address | Specifies the module address for Modbus command control | 1 (x0001)
1…255 |
| x4002 | Coils | Contains a value specifying the number of outputs
(Coils) available in the module. |
16 (x0010) |
| x4004 | Inputs | Contains a value specifying the number of inputs (Discrete inputs) available in the module. Read-only value |
0 (x0000) |
| x4006 | Baud | Specifies the RS485 communication speed (baud rate). Value without the last 2 zeros, e.g.: 1200 = 12 = x000C; 2400 = 24 = x0018 4800 = 48 = x0030; 9600 = 96 = x0060 19200 = 192 = x00C0; 57600 = 576 = x0240 115200 = 1152 = x0480; 256000 = 2560 = x0A00 |
192 (x00C0)
12…10000 |
| x4008 | Parity | Specifies the parity for RS485 communication. 0 - none; 1 - even; 2 - odd |
0 (x0000)
0…2 |
| x400A | Stop | Specifies the number of stop bits for RS485 communication. 1 - 1 stop bit; 2 - 2 stop bits |
1 (x0001)
1…2 |
| x400C | Broadcast | Defines whether the device executes
commands with the broadcast address value of 0 (x00). 0 - no, 1 - yes |
1 (x0001)
0…1 |
| x400E | CRC | Defines whether the device verifies the checksum in Modbus commands. 0 - no, 1 - yes | 0 (x0000)
0…1 |
| x4010 | Response | Enables sending responses to Modbus commands.
0 - does not send any responses, 1 - sends responses to Modbus commands |
1 (x0001)
0…1 |
| x4012 | IO Offset | Specifies the starting index for inputs and outputs (coils)
0 - inputs/outputs start from 0 (0…15) 1 - inputs/outputs start from 1 (1…16) |
1 (x0001)
0…1 |
| x4014
and x8000 |
Version | Contains the firmware version.
A value of 10 indicates version 1.0, etc. Read-only value |
10 (x00A0) |
| x2000 | ExBaud | Allows setting communication parameters using one of the predefined values.
The low byte corresponds to the baud rate: 0 - 4800, 1 - 9600, 2 - 19200, 3 - 38400 4 - 57600, 5 - 115200, 6 - 12800, 7 - 256000 8 - other value The high byte specifies the parity: 0 - none, 1 - even, 2 - odd |
x0002
x0000…x0208 |
Measurement Input Registers (Input Registers)
The device is equipped with measurement circuits for power supply voltage and temperature, which allow monitoring of the module's operating conditions to prevent failures. The measurement results are available in the measurement input registers, known as Input Registers. These registers can be read using Modbus commands.
| Register Number (hex) | Name | Description | Value Range |
|---|---|---|---|
| x3000 | Voltage | Measurement of the power supply voltage. A value of 495 = 4.95 V, etc. | 330…550 |
| x3002 | Temp | Measurement of the module temperature. A temperature value of 24 (x0018) indicates 24 degrees C. Temperature range: -20…-1 is stored as xFF14…xFF01 Temperature range: 0…70 is stored as x0000…x0046 |
-20…-1 *C = xFF14…xFF01 0…70 *C = x0000…0046 |
Modbus Standard Control Commands
Each command in the Modbus standard takes the form of a data frame, the structure of which is shown in the figure:
Consecutive frames must be separated by an interval of at least 3.5 character times (the time required to transmit a full ASCII character), whereas the interval between transmitting one character and starting the transmission of the next within the same frame must not exceed 1.5 character times. These rules apply for communication speeds (baud rates) up to 19200.
If the communication speed is set above 19200, the minimum interval between frames has a fixed value equal to 1.75 ms. Meanwhile, the interval between consecutive characters of the same frame must not exceed 0.75 ms.
Each device connected to the Modbus bus must be assigned a unique address. The address field is present in every transmitted frame, has a size of 1 byte, and can have a value in the range of 1…255. An address value of 0 is the so-called broadcast address and allows directing a command to all devices connected to the bus. In some systems, it is recommended not to set addresses above the value of 247.
Outputs and inputs are standardly numbered from 1. In this case, the first output is output number 1 (x01), and the last one is number 16 (0x10). The command descriptions and command examples refer specifically to this variant. However, the device can be configured in such a way that the outputs and inputs are numbered from 0. In that case, the first output is output number 0 (x00), and the last one is number 15 (0x0F). If the output number referenced by the control/read command exceeds the number of outputs contained in the device (15 or 16, depending on configuration), the command will not be executed and will remain unanswered.
The Modbus standard includes several standard commands. Each of them, along with example commands and device responses, is described in the subsequent section of this manual.
List of Supported Modbus Commands
| Command Name | Command Code | Function |
|---|---|---|
| Write Single Coil | x05 | Allows controlling the state of an output or outputs |
| Write Multiple Coils | x0F | Allows controlling the state of multiple outputs simultaneously, both turning specific outputs ON and OFF. |
| Read Coils | x01 | Allows reading the state of an output or outputs |
| Read Discrete Inputs | x02 | Allows reading the state of inputs. Since the
Modig Modbus 16R device does not have inputs for reading states, it reads the state of the outputs in response to this command, similarly to the “Read Coils” - x01 command. |
| Read Input Registers | x04 | Allows reading values from the measurement input registers |
| Read Holding Registers | x03 | Allows reading values from the configuration registers |
| Write Single Holding Register | x06 | Allows setting a value in a configuration register |
| Write Multiple Holding Registers | x10 | Allows setting values in several configuration registers |
“Write Single Coil” Command - x05
The x05 command allows controlling the state of an output or outputs.
| Data frame with x05 command | 01 05 00 00 FF 00 8C 3A | |
|---|---|---|
| Byte Number | Value (hex) | Meaning |
| 1 | x01 | Target device address |
| 2 | x05 | “Write Single Coil” command - control of a single output |
| 3…4 | x0000 | Number of the output to be controlled:
0 - none of the outputs, 1 - output 1 (first), 16 - output 16 (last) x00FF - controls all outputs - from 1 to 16 |
| 5…6 | xFF00 | Value specifying the task to be executed:
x0000 - turn off (OFF), xFF00 - turn on (ON), x5500 - toggle state to the opposite (TOGGLE) ON->OFF / OFF->ON |
| 7…8 | x8C3A | CRC16 checksum |
| Response | The device that reads and executes
the command will send an identical frame in response: | |
Similar commands:
- A5 05 00 08 55 00 6A 7C - x05 command to the device with address 165
(xA5), output no. 8 (x0008) will toggle its state (x5500)
- Response: A5 05 00 08 55 00 6A 7C
- 14 05 00 10 00 00 CE CA - x05 command to the device with address 20
(x14), output no. 16 (x0010) will be turned OFF (x0000)
- Response: 14 05 00 10 00 00 CE CA
- 29 05 00 FF FF 00 BA 22 - x05 command to the device with address 41
(x29), all outputs (x00FF) will be turned ON (xFF00)
- Response: 29 05 00 FF FF 00 BA 22
“Write Multiple Coils” Command - x0F
The x0F command allows controlling the state of multiple outputs simultaneously, both turning specific outputs ON and OFF.
| Data frame with x0F command | 01 0F 00 01 00 03 02 00 05 27 76 | |
|---|---|---|
| Byte Number | Value (hex) | Meaning |
| 1 | x01 | Target device address |
| 2 | x0F | “Write Multiple Coils” command - control of multiple outputs |
| 3…4 | x0001 | Number of the output from which control will begin:
0 - none of the outputs will be controlled, 1 - from output 1 (first), 16 - from output 16 (last) |
| 5…6 | x0003 | Number of outputs to be controlled:
0 - none of the outputs will be controlled 1 - one output, 16 - to control 16 outputs |
| 7 | x02 | Number of data bytes containing the control sequence - must be 2 |
| 8…9 | x0005 | Control sequence, LSB -> output no. 1.
Bits with a value of 0 cause outputs to turn off, bits with a value of 1 cause outputs to turn on. x0005 = 00000000 00000101 - outputs 1 and 3 turned ON |
| 10...11 | x27 76 | CRC16 checksum |
| Response | The device that reads and executes the command will send the following frame in response:
| |
| 1 | x01 | Address of the responding device |
| 2 | x0F | “Write Multiple Coils” command - output control |
| 3...4 | x0001 | Number of the output from which control was initiated |
| 5...6 | x0003 | Number of outputs that were actually controlled |
| 7...8 | x440A | CRC16 checksum |
If the number of outputs to be set exceeds the number of outputs contained in the device (after considering the starting output number from which control begins), the command will be executed correctly for the existing outputs. The response will return the number of outputs actually controlled.
Similar commands:
- A5 0F 00 08 00 04 02 00 07 6D 9D - x0F command to the device with
address 165 (xA5), controls 3 (x0003) outputs starting from output no. 8 (x0008),
the control sequence is: x0007 (00000000 00000111), meaning it will turn ON outputs 8, 9, 10 and turn OFF output 11.
- Response: A5 0F 00 08 00 04 CC EE
- 14 0F 00 0F 00 05 02 00 00 14 43 - x0F command to the device with
address 20 (x14), controls 5 (x0005) outputs starting from output no. 15 (x000F),
the control sequence is: x0000 (00000000 00000000), meaning it will turn OFF outputs 15 and 16.
- Response: 14 0F 00 0F 00 02 E6 CC (2 outputs controlled instead of 5)
- 29 0F 00 01 00 10 02 FF FF 1C 40 - x0F command to the device with
address 41 (x29), controls 16 (x0010) outputs starting from output no. 1 (x0001),
the control sequence is xFFFF (11111111 11111111), meaning it will turn ON all outputs from 1 to 16.
- Response: 29 0F 00 01 00 10 03 EF
“Read Coils” Command - x01
The x01 command allows reading the state of an output or outputs.
| Data frame with x01 command | 01 01 00 02 00 04 9C 09 | |
|---|---|---|
| Byte Number | Value (hex) | Meaning |
| 1 | x01 | Target device address |
| 2 | x01 | “Read Coils” command - reading output states |
| 3…4 | x0002 | Number of the output from which reading of output states will begin:
2 - read starting from output no. 2 |
| 5…6 | x0004 | Value specifying how many outputs will be read:
4 - reading 4 outputs, namely: 2, 3, 4, and 5 |
| 7…8 | x9C09 | CRC16 checksum |
| Response | The device that reads and executes
the command will send the following frame in response: | |
| 1 | x01 | Address of the responding device |
| 2 | x01 | “Read Coils” command - reading output states |
| 3 | x02 | Number of data bytes containing the response - 2 |
| 4…5 | x000C | Output states: 2 - OFF (0), 3 - OFF (0), 4 - ON (1), 5 - ON (1)
Binary: 00000000 00001100 |
| 6…7 | xB9F9 | CRC16 checksum |
Similar commands:
- A5 01 00 08 00 06 6A 7C - x01 command to the device with address 165
(xA5), reading the state of 6 (x0006) outputs, starting from output 8 (x0008).
- Response: A5 01 02 00 02 49 E4 - only output no. 9 is active (x0002)
- 14 01 00 10 00 01 CE CA - x01 command to the device with address 20
(x14), reading the state of one (x0001) output, starting from output 16 (x0010).
- Response: 14 01 02 00 00 B4 3F - output turned off (x0000)
- 29 01 00 20 01 00 BA 06 - x01 command to the device with address 41
(x29), reading the state of 16 (x0010) outputs, starting from output 32 (x0020).
- Response: no response - cannot read states starting from output 32
If the number of outputs to be read exceeds the number of outputs contained in the device (after considering the starting output number from which the status reading begins), non-existent outputs in the response will always have an OFF (0) state.
“Read Discrete Inputs” Command - x02
The x02 command allows reading the state of inputs. Since the Modig Modbus 16R device does not have inputs for reading states, it reads the state of the outputs in response to this command, similarly to the “Read Coils” - x01 command.
| Data frame with x02 command | 01 02 00 02 00 04 D8 09 | |
|---|---|---|
| Byte Number | Value (hex) | Meaning |
| 1 | x01 | Target device address |
| 2 | x02 | “Read Discrete Inputs” command - reading input states |
| 3…4 | x0002 | Number of the input from which reading of input states will begin:
2 - read starting from input no. 2 |
| 5…6 | x0004 | Value specifying how many inputs will be read:
4 - reading 4 inputs, namely: 2, 3, 4, and 5 |
| 7…8 | xD809 | CRC16 checksum |
| Response | The device that reads and executes
the command will send the following frame in response: | |
| 1 | x01 | Address of the responding device |
| 2 | x02 | “Read Discrete Inputs” command - reading input states |
| 3 | x02 | Number of data bytes containing the response - 2 |
| 4…5 | x000C | Input states: 2 - inactive (0), 3 - inactive (0), 4 - active (1), 5 - active (1);
Binary: 00000000 00001100 |
| 6…7 | xB9BD | CRC16 checksum |
Similar commands:
- A5 02 00 08 00 06 60 EE - x02 command to the device with address 165
(xA5), reading the state of 6 (x0006) inputs, starting from input 8 (x0008).
- Response: A5 02 02 00 02 49 A0 - only input no. 9 is active (x0002)
- 14 02 00 10 00 01 BA CA - x02 command to the device with address 20
(x14), reading the state of one (x0001) input, starting from input 16 (x0010).
- Response: 14 02 02 00 00 B4 7B - input inactive (x0000)
- 29 02 00 20 01 00 7E 78 - x02 command to the device with address 41
(x29), reading the state of 16 (x0010) inputs, starting from input 32 (x0020).
- Response: no response - cannot read states starting from input 32
If the number of inputs to be read exceeds the number of inputs contained in the device (after considering the starting input number from which the status reading begins), non-existent inputs in the response will always have an inactive (0) state.
“Read Input Registers” Command - x04
The x04 command allows reading values from the measurement input registers. The Modig Modbus 16R device supports measurement of the power supply voltage and the module temperature.
| Data frame with x04 command | 01 04 30 00 00 02 7E CB | |
|---|---|---|
| Byte Number | Value (hex) | Meaning |
| 1 | x01 | Target device address |
| 2 | x04 | “Read Input Registers” command - reading measurement input registers |
| 3…4 | x3000 | Number of the register from which reading will begin.
x3000 - reading the power supply voltage measurement x3002 - reading the module temperature measurement |
| 5…6 | x0002 | Value specifying how many registers will be read:
1 - one, e.g., voltage only; 2 - both measurement registers |
| 7…8 | x7ECB | CRC16 checksum |
| Response | The device that reads and executes
the command will send the following frame in response: | |
| 1 | x01 | Address of the responding device |
| 2 | x04 | “Read Input Registers” command - reading measurement input registers |
| 3 | x04 | Number of data bytes containing the response - 4 |
| 4…5 | x0206 | Voltage value - x0206 = 518, which means 5.18 V |
| 6…7 | x0018 | Temperature value - x0018 = 24, which means 24 degrees C
Temperature range: -20…-1 is stored as xFF14…xFF01 Temperature range: 0…70 is stored as x0000…x0046 |
| 8…9 | x1A37 | CRC16 checksum |
Similar commands:
- A5 04 30 00 00 01 27 EE - x04 command to the device with address 165
(xA5), reading one register (x0001) numbered x3000, i.e., the power supply voltage measurement register.
- Response: A5 04 02 01 F0 49 A0 - voltage is 4.96 V (x01F0 = 496)
- 14 04 30 08 00 02 FD CC - x04 command to the device with address 20
(x14), reading two (x0002) measurement registers starting from number x3008.
- Response: no response - there is no measurement register with the number x3008.
- 29 04 30 02 00 02 7E 78 - x04 command to the device with address 41
(x29), reading two (x0002) measurement registers starting from number x3002.
- Response: A5 04 02 00 18 C8 E3 - the device has no measurement registers
higher than x3002, therefore only one register was read (number x3002) - module temperature = 24 (x0018), and the response contains only two data bytes (x02)
“Read Holding Registers” Command - x03
The x03 command allows reading values from the configuration registers.
| Data frame with x03 command | 01 03 40 00 00 01 91 CA | |
|---|---|---|
| Byte Number | Value (hex) | Meaning |
| 1 | x01 | Target device address |
| 2 | x03 | “Read Holding Registers” command - reading configuration registers |
| 3…4 | x4000 | Number of the register from which reading will begin.
Available registers are in the ranges x4000…x4014 as well as x2000 and x8000 |
| 5…6 | x0001 | Value specifying how many registers will be read:
1 - one, etc., up to a maximum of 8 |
| 7…8 | x91CA | CRC16 checksum |
| Response | The device that reads and executes
the command will send the following frame in response: | |
| 1 | x01 | Address of the responding device |
| 2 | x03 | “Read Holding Registers” command - reading configuration registers |
| 3 | x02 | Number of data bytes containing the response - 2 |
| 4…5 | x0001 | Register number x4000 contains the address for Modbus commands, which in this case is 1 (x0001) |
| 6…7 | x7984 | CRC16 checksum |
Similar commands:
- A5 03 40 06 00 04 28 EE - x03 command to the device with address 165
(xA5), reading four configuration registers (x0004) starting from number (x4006).
- Response: 01 03 08 00 C0 00 00 00 01 00 01 C5 DB - values of 4 configuration registers, meaning 8 data bytes
- 14 03 80 00 00 01 AF 0F - x03 command to the device with address 20
(x14), reading one (x0001) configuration register numbered x8000, i.e., the firmware version.
- Response: 14 03 02 00 A0 B5 FF - response of 2 bytes (x00A0) = 10, indicating firmware version 1.0
“Write Single Holding Register” Command - x06
The x06 command allows setting a value in a configuration register.
| Data frame with x06 command | 01 06 40 00 00 01 5D CA | |
|---|---|---|
| Byte Number | Value (hex) | Meaning |
| 1 | x01 | Target device address |
| 2 | x06 | “Write Single Holding Register” command - writing a configuration register |
| 3…4 | x4000 | Number of the register to which the new value will be written.
Available registers are in the ranges x4000, x4006…x4012, and x2000 |
| 5…6 | x0001 | Value to be written to the register |
| 7…8 | x5DCA | CRC16 checksum |
| Response | The device that reads and executes
the command will send an identical frame in response: | |
Similar commands:
- A5 06 40 00 00 04 84 ED - x06 command to the device with address 165
(xA5), writing a value of 4 (x0004) to the configuration register numbered x4000, i.e., assigning a new address of 4.
- Response: A5 06 40 00 00 04 84 ED
- 14 06 40 0C 00 00 5E CC - x06 command to the device with address 20
(x14), writing a value of 0 (x0000) to the configuration register numbered x400C, i.e., disabling broadcast command handling.
- Response: 14 06 40 0C 00 00 5E CC
“Write Multiple Holding Registers” Command - x10
The x10 command allows setting values in several configuration registers.
| Data frame with x10 command | 01 10 40 0C 00 03 06 00 01 00 00 00 01 8F 7E | |
|---|---|---|
| Byte Number | Value (hex) | Meaning |
| 1 | x01 | Target device address |
| 2 | x10 | “Write Multiple Holding Registers” command - writing several configuration registers |
| 3…4 | x400C | Number of the register from which writing will begin.
Available registers are in the ranges x4000, x4006…x4012, and x2000 |
| 5…6 | x0003 | Value specifying how many registers will be written:
1 - one, etc., up to a maximum of 8 |
| 7 | x06 | Number of data bytes containing the values to be written |
| 8…13 | x0001 x0000 x0001 |
Three values to be written into the configuration registers |
| 14…17 | x8F7E | CRC16 checksum |
| Response | The device that reads and executes
the command will send the following frame in response: 03 55 CB | |
| 1 | x01 | Address of the responding device |
| 2 | x10 | “Write Multiple Holding Registers” command - writing several configuration registers |
| 3...4 | x400C | Number of the register from which the value writing was initiated |
| 5...6 | x0003 | style="text-align |