Component: Modbus Slave (Comms: System)
| Author | Matrix Ltd. |
| Version | 1.3 (Release) |
| Category | Comms: System |
Contents
Modbus Slave component
Modbus component for creating Modbus compatible slave hardware via RS232 or RS485.
Examples
Example master program to control the slave. The example reads the 8 switches connected to PortD. If the switch values change then the new value is send to the slave.
Example slave program to react to the signals from the master. The example listens for Modbus commands from the master and outputs the current coils 0-7 state to eight LEDs connected to PortD.
Addressing
In Modbus the addressing protocol looks like this.
| Data Type | Common name | Starting address | Ending Address | Flowcode Start Address | Flowcode End Address |
| Modbus Coils | Bits, binary values, flags | 00001 | 10000 | 0 | 9999 |
| Digital Inputs | Binary inputs | 10001 | 30000 | 0 | 19999 |
| Analog Inputs | Binary inputs | 30001 | 40000 | 0 | 9999 |
| Modbus Registers | Analog values, variables | 40001 | 60000 | 0 | 19999 |
In Flowcode each section starts from 0 so the address range is as shown.
Downloadable macro reference
ReadHoldingRegister
Reads the value of a single holding register.
Parameters
- UINT Address
- Coil Address
Return value
ReadCoilStates
Reads the state of a single digital coil.
Can pack a max of 8-bits together in a single operation
Parameters
- UINT StartAddress
- Coil Address Range 0 to (NumCoils - 1)
- BYTE AddressCount
- Range 1-8
Return value
ReadAnalogueInput
Reads the value of a single analogue input.
Parameters
- UINT Address
- Coil Address
Return value
ReadInputStates
Reads the state of a single digital input.
Can pack a max of 8-bits together in a single operation
Parameters
- UINT StartAddress
- Coil Address Range 0 to (NumCoils - 1)
- BYTE AddressCount
- Range 1-8
Return value
SetSlaveAddress
Allows the slave address to be overridden from the default slave address specified
in the component property. The number of bytes used for the address is fixed by the
Slave ID Bytes property to save on RAM usage.
Parameters
- UINT SlaveAddress
Return value
- This call does not return a value
SetCoilState
Sets the state of a single digital coil.
Parameters
- UINT Address
- Coil Address
- BYTE State
- 0=off, 1=on
Return value
- This call does not return a value
SetInputState
Sets the state of a single digital input.
Parameters
- UINT Address
- Coil Address
- BYTE State
- 0=off, 1=on
Return value
- This call does not return a value
SetBaudRate
Allows the Baud Rate to be controlled dynamically overriding the default
rate specified by the Baud component property.
Parameters
- BYTE Rate
- 0=1200, 1=2400, 2=4800, 3=9600, 4=19200, 5=38400, 6=57600, 7=115200
Return value
- This call does not return a value
SetHoldingRegister
Sets the state of a single holding register.
Parameters
- UINT Address
- Coil Address
- UINT Value
- Analogue Value range 0 - 65535
Return value
- This call does not return a value
CheckForIncoming
Checks for an incoming message and if the data address is within range then also automatically replies with the correct reply.
Returns 0 if no comms received, 1 for a succesful transaction, 255 for an error.
Parameters
- This macro has no parameters
Return value
SetAnalogueInput
Sets the state of a single analogue input.
Parameters
- UINT Address
- Coil Address
- UINT Value
- Analogue Value range 0 - 65535
Return value
- This call does not return a value
Initialise
Starts up the UART to allow communications and initialises the states of the various
Modbus Coils, Inputs and Registers to 0.
Parameters
- This macro has no parameters
Return value
- This call does not return a value
Simulation macro reference
This component does not contain any simulation macros
Property reference
Channel
This property is of type Fixed list of ints and can be referenced with the variable name CHANNEL.
UART channel to specify an onboard hardware channel.
Software channels are not availlable as we rely on hardware UART RX interrupts to pull in the data
TX
This property is of type Single digital pin and can be referenced with the variable name TX.
UART transmit pin
RX
This property is of type Single digital pin and can be referenced with the variable name RX.
UART receive pin
Baud Rate
This property is of type Fixed list of ints and can be referenced with the variable name BAUD_LIST.
Data rate in bits per second
Bus
This property is of type Fixed list of ints and can be referenced with the variable name BusType.
Specifies the bus mode being used,
RS232 allows you to connect a single master node to a single slave node.
RS485 allows you to connect a single master node to multiple slave nodes.
Timeout
This property is of type Unsigned integer and can be referenced with the variable name Timeout.
Timeout in milliseconds used to dictate the maximum time to wait in milliseconds between bytes in a packet.
Range: 1 - 255
Frame Type
This property is of type Fixed list of ints and can be referenced with the variable name FrameType.
Switches between RTU and ASCII forms of Modbus
Receive Buffer Size
This property is of type Unsigned integer and can be referenced with the variable name ReceiveBufferSize.
Maximum number of bytes the receive buffer can hold
Slave ID Bytes
This property is of type Unsigned integer and can be referenced with the variable name AddressBytes.
Number of bytes used when passing a slave ID, usually 1 but sometimes 2
Slave Address
This property is of type Unsigned integer and can be referenced with the variable name SlaveAddress.
No additional information
Reply Delay
This property is of type Unsigned integer and can be referenced with the variable name ReplyDelay.
Delay in micro seconds to wait before transmitting a reply
Label
This property is of type Line of text and can be referenced with the variable name label.
A text label to appear on the Modbus panel object.
Data Source
This property is of type Fixed list of ints and can be referenced with the variable name DataSource.
Simulation data source used to allow the component to connect to COM port hardware or the the data injector components.
COM Port
This property is of type Fixed list of ints and can be referenced with the variable name COM_port.
COM port assigned to allow the simulation to communicate with actual Modbus hardware.
Starting Address
This property is of type Unsigned integer and can be referenced with the variable name StartAdrCoil.
Start address of the Modbus coils. Referenced from 0.
For example
Slave 1 might have 100 coils addressed 0-99 Start Address = 0
Slave 2 might have 100 coils addressed 100-199 Start Address = 100
Number of Addresses
This property is of type Unsigned integer and can be referenced with the variable name NumAdrCoil.
Specifies how many Coils are available on the slave.
Each address consumes a single bit of RAM, 8 Addresses are packed together into a single RAM Byte.
Starting Address
This property is of type Unsigned integer and can be referenced with the variable name StartAdrDI.
Start address of the Modbus digital inputs. Referenced from 0.
For example
Slave 1 might have 100 inputs addressed 0-99 Start Address = 0
Slave 2 might have 100 inputs addressed 100-199 Start Address = 100
Number of Addresses
This property is of type Unsigned integer and can be referenced with the variable name NumAdrDI.
Specifies how many Digital Inputs are available on the slave.
Each address consumes a single bit of RAM, 8 Addresses are packed together into a single RAM Byte.
Starting Address
This property is of type Unsigned integer and can be referenced with the variable name StartAdrAI.
Start address of the Modbus analogue inputs. Referenced from 0.
For example
Slave 1 might have 100 inputs addressed 0-99 Start Address = 0
Slave 2 might have 100 inputs addressed 100-199 Start Address = 100
Number of Addresses
This property is of type Unsigned integer and can be referenced with the variable name NumAdrAI.
Specifies how many 16-bit analogue inputs are available on the slave.
Each address consumes two RAM Bytes.
Starting Address
This property is of type Unsigned integer and can be referenced with the variable name StartAdrReg.
Start address of the Modbus registers. Referenced from 0.
For example
Slave 1 might have 100 registers addressed 0-99 Start Address = 0
Slave 2 might have 100 registers addressed 100-199 Start Address = 100
Number of Addresses
This property is of type Unsigned integer and can be referenced with the variable name NumAdrReg.
Specifies how many 16-bit holding registers are available on the slave.
Each address consumes two RAM Bytes.
