Component: Modbus Slave (Comms: System)

Author	Matrix Ltd.
Version	2.0 (Release)
Category	Comms: System

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. 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

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

UINT

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

BYTE

ReadAnalogueInput

Reads the value of a single analogue input.

Parameters

UINT Address

Coil Address

Return value

UINT

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

BYTE

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

ChangeFrameType

Default frame type is the type set in the component properties.

Parameters

BYTE Type

0 = Modbus RTU / 1 = Modbus ASCII

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

BYTE

ChangeBaud

Changes the UART Baud rate.

1 = 1200 / 2 = 2400 / 3 = 4800 / 4 = 9600 / 5 = 19200 / 6 = 31250

7 = 38400 / 8 = 57600 / 9 = 115200

Parameters

BYTE Baud

The new baud rate (0=1200, 9=115200)

Return value

This call does not return a 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 cal_uart::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

This property is of type Single digital pin and can be referenced with the variable name cal_uart::TX.

Pin to be used for Transmit data

RX

This property is of type Single digital pin and can be referenced with the variable name cal_uart::RX.

Pin to be used for Receive data

Baud Options

This property is of type Fixed list of ints and can be referenced with the variable name cal_uart::BAUD_LIST.

Baud rate option selector

Baud Rate

This property is of type Signed integer and can be referenced with the variable name cal_uart::BAUD.

No additional information

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.

Scope Traces

This property is of type True or false and can be referenced with the variable name cal_uart::ScopeTraces.

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

This property is of type True or false and can be referenced with the variable name cal_uart::ConsoleData.

Selects if the console data is automatically generated or not

Console Columns

This property is of type Unsigned integer and can be referenced with the variable name cal_uart::ConsoleColumns.

Number of characters that can be displayed on a single line of the console.

Data Source

This property is of type Fixed list of ints and can be referenced with the variable name cal_uart::DataSource.

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 

   Injector - Routes the communication data via a data injector component on the Panel.

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.