Component: Modbus Slave (Comms: System)

Author	Matrix Ltd.
Version	2.0
Category	Comms: System

Modbus Slave component

Modbus component for creating Modbus compatible slave hardware via RS232 or RS485.

Detailed description

No detailed description exists yet for this component

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.

Modbus Master Example

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.

Modbus Slave Example

Master and Slave example using vNet

Example of communicating using Modbus Master and Slave using two instances of Flowcode and the vNet injector component.

ModbusMasterDemo

ModBusSlaveDemo

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.

Macro reference

ChangeBaud

	ChangeBaud
Changes the UART Baud rate. 1 = 1200 / 2 = 2400 / 3 = 4800 / 4 = 9600 / 5 = 19200 / 6 = 31250 7 = 38400 / 8 = 57600 / 9 = 115200
- BYTE	Baud
The new baud rate (0=1200, 9=115200)
- VOID	Return

ChangeFrameType

	ChangeFrameType
Default frame type is the type set in the component properties.
- BYTE	Type
0 = Modbus RTU / 1 = Modbus ASCII
- VOID	Return

CheckForIncoming

	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.
- BYTE	Return

GetLastIncoming

	GetLastIncoming
Gets a value from the last incoming command. Index 0 = 0 Read / 1 Write Index 1 = 0 Coils / 1 DigInput / 2 AnInput / 3 Register Index 2 = Address Index 3 = Number
- BYTE	Index
Range: 0-3
- UINT	Return

Initialise

	Initialise
Starts up the UART to allow communications and initialises the states of the various Modbus Coils, Inputs and Registers to 0.
- VOID	Return

ReadAnalogInput

	ReadAnalogInput
Reads the value of a single analogue input.
- UINT	Address
Coil Address
- UINT	Return

ReadCoils

	ReadCoils
Reads the state of up to eight digital coils. Can pack a max of 8-bits together in a single operation
- UINT	StartAddress
Coil Address Range 0 to (NumCoils - 1)
- BYTE	AddressCount
Range 1-8
- BYTE	Return

ReadDigitalInputs

	ReadDigitalInputs
Reads the state of up to eight digital inputs. Can pack a max of 8-bits together in a single operation
- UINT	StartAddress
Coil Address Range 0 to (NumCoils - 1)
- BYTE	AddressCount
Range 1-8
- BYTE	Return

ReadHoldingRegister

	ReadHoldingRegister
Reads the value of a single holding register.
- UINT	Address
Coil Address
- UINT	Return

SetAnalogInput

	SetAnalogInput
Sets the state of a single analogue input.
- UINT	Address
Coil Address
- UINT	Value
Analogue Value range 0 - 65535
- VOID	Return

SetBaudRate

	SetBaudRate
Allows the Baud Rate to be controlled dynamically overriding the default rate specified by the Baud component property.
- BYTE	Rate
0=1200, 1=2400, 2=4800, 3=9600, 4=19200, 5=38400, 6=57600, 7=115200
- VOID	Return

SetCoil

	SetCoil
Sets the state of a single digital coil.
- UINT	Address
Coil Address
- BYTE	State
0=off, 1=on
- VOID	Return

SetDigitalInput

	SetDigitalInput
Sets the state of a single digital input.
- UINT	Address
Coil Address
- BYTE	State
0=off, 1=on
- VOID	Return

SetHoldingRegister

	SetHoldingRegister
Sets the state of a single holding register.
- UINT	Address
Coil Address
- UINT	Value
Analogue Value range 0 - 65535
- VOID	Return

SetSlaveAddress

	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.
- UINT	SlaveAddress
- VOID	Return

Property reference

	Properties
	UART Properties
	Channel
UART Channel selector Software channels are bit banged using generic I/O pins but are not as reliable as hardware channels. Hardware channels use the selected peripheral on-board the target microcontroller.
	TX
Pin to be used for Transmit data
	RX
Pin to be used for Receive data
	Baud Options
Baud rate option selector
	Baud Rate
	Bus
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
Timeout in milliseconds used to dictate the maximum time to wait in milliseconds between bytes in a packet. Range: 1 - 255
	Modbus Properties
	Frame Type
Switches between RTU and ASCII forms of Modbus
	Receive Buffer Size
Maximum number of bytes the receive buffer can hold
	Slave ID Bytes
Number of bytes used when passing a slave ID, usually 1 but sometimes 2
	Slave Address
	Reply Delay
Delay in micro seconds to wait before transmitting a reply
	Maintain Stats
Controls if the last command from the master is logged allowing for easier value updates. No - Do not log commands Yes - Commands are logged and available via the GetLastIncoming macro
	Simulation Properties
	Label
A text label to appear on the Modbus panel object.
	Scope Traces
Selects if the scope traces are automatically added to the data recorder window or not. Simulation - draws an approximation of the UART data onto the scope trace. ICT - sets up the scope trace for incoming data and adds UART packet decoding at the correct BAUD.
	Console Data
Selects if the console data is automatically generated or not
	Console Columns
Number of characters that can be displayed on a single line of the console.
	Data Source
Simulation data source used to allow the component to connect to various remote devices Nothing - Simulation data is ignored COM port - Routes the communication data to and from a physical or virtual COM port API - Routes the communication data via a data API component on the Panel.
	API
Selects which API component to route the communication data via. Add API components to the panel before they will be available in this list. API components are available from the Comms component category.
	Modbus Coils - Single bit values
	Starting Address
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
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.
	Digital Inputs - Single bit values
	Starting Address
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
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.
	Analog Inputs - 16-bit values
	Starting Address
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
Specifies how many 16-bit analogue inputs are available on the slave. Each address consumes two RAM Bytes.
	Holding Registers - 16-bit values
	Starting Address
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
Specifies how many 16-bit holding registers are available on the slave. Each address consumes two RAM Bytes.

Component Source Code

Please click here to download the component source project: FC_Comp_Source_ModbusSlave.fcfx

Please click here to view the component source code (Beta): FC_Comp_Source_ModbusSlave.fcfx