Component: Modbus Slave USB (Comms: System)

Author	Matrix Ltd.
Version	2.0
Category	Comms: System

Modbus Slave USB component

Modbus component for creating Modbus compatible slave hardware via USB Serial.

Component Source Code

Please click here for the component source code: FC_Comp_Source_ModbusSlaveUSB.fcfx

Detailed description

No detailed description exists yet for this component

Examples

Example master program to control the slave. The example sets coil address 0, clears coil address 0, reads an input register and outputs to the LCD. Be sure to set the IP address of the slave device at the top of the program. If you are simulating then use the IP address of the PC running the Slave simulation. Both programs can be simulated on the same PC using two instances of Flowcode.

Modbus TCP 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 state to an LED connected to PortA. The input register is loaded with a value which is incremented on each Modbus transaction.

Modbus TCP Slave Example

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.
- UINT	Address
Coil Address
- UINT	Return

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

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

	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

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

	ReadCoils
Reads the state of a single digital coil. 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

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

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

	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

	ReadDigitalInputs
Reads the state of a single digital input. 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

	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

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

	Initialise
Starts up the UART to allow communications and initialises the states of the various Modbus Coils, Inputs and Registers to 0. Returns 1 if USB is started ok.
- BOOL	Return

Property reference

	Properties
	USB Properties
	USB Properties
	Vendor ID
USB VID
	Product ID
USB PID
	Device Name
USB Device Name
	Manufacturer
USB Manufacturer
	Major Version
USB Major Version Number
	Minor Version
USB Minor Version Number
	Return Type
Specifies the way the receive function indicates a timeout. 8 Bit mode - Timeout is represented by the value 255. 16 Bit mode - Timeout is represented by the value 512 allowing the value 255 to represent valid data
	Enumeration Timeout
Specifies if the enumeration (Initialise function) can timeout if taking too long.
	USB Driver
	Driver Directory
Directory to save the generated device driver .inf file
	Driver Filename
Filename to give to the generated driver file.
	Generate Driver
Generates a driver file when set to Yes, Automatically jumps back to No when complete.
	Modbus Properties
	Timeout
Timeout in milliseconds used to dictate the maximum time to wait in milliseconds between bytes in a packet. Range: 1 - 255
	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.
	COM Port
Hardware COM port to communicate with any connected USB serial devices or any other virtual COM ports.
	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.