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ModbusSlaveNode.readHoldingRegister()

[Modbus]

Description

Reads the Holding Registers register.

Syntax

node1.readHoldingRegister(address)
node2.readHoldingRegister(address, size, buffer)

Parameters

  • node1/node2: ModbusSlaveNode object.
  • address: Address of the Holding Registers to be read.
  • size: The number of Holding Registers to be read.
  • buffer: Copy the read-out Holding Registers data to the array space pointed to by the buffer.

Returns

int: The HoldingRegister location data is returned when only the address pointer is used.

If the specified buffer is used, MODBUS_SUCCESS is returned, and EXCEPTION_CODE is returned.

Example

#include <Modbus86.h>
 
ModbusSlave bus;
ModbusSlaveNode node;
 
uint32_t command = 0;
uint32_t lasttime = 0;
 
uint8_t read_holding_registers( uint8_t function,
                                uint16_t address,
                                uint16_t length)
{
    for (int i = address; i < address + length; i++) {
        if (i == 16)
            node.writeHoldingRegister(i, command & 0xFFFF);
        else if (i == 17)
            node.writeHoldingRegister(i, (command >> 16) & 0xFFFF);
    }
     
    return MODBUS_SUCCESS;
}
 
uint8_t write_multiple_registers(   uint8_t function,
                                    uint16_t address,
                                    uint16_t length)
{
    int i;
 
    for (i = address; i < address + length; i++) {
        if (i == 16)
            command = (command & 0xFFFF0000) | node.readHoldingRegister(i);
        else if (i == 17)
            command = 
                (command & 0x0000FFFF) | (node.readHoldingRegister(i) << 16);
    }
 
    return MODBUS_SUCCESS;
}
 
void setup()
{    
    Serial485.begin(115200);
     
    /* Modbus RTU Mode via RS485. */
    bus.begin(MODBUS_RTU, Serial485);
     
    /* Slave node with ID 11. */
    node.attach(11, bus);
 
    /* Set the callback function of Read Holding Registers (0x03). */
    node.cbFunc[MODBUS_CB_READ_HOLDING_REGISTERS]
                            = read_holding_registers;
                             
    /* Set the callback function of Write Multiple Registers (0x10). */
    node.cbFunc[MODBUS_CB_WRITE_MULTIPLE_REGISTERS]
                            = write_multiple_registers;
}
 
void loop()
{
    uint32_t now;
     
    node.poll();
     
    now = millis();
    if (now - lasttime > 500) {
        lasttime = now;
        Serial.print("commnad = ");
        Serial.println(command);
    }
}

See Also

Libraries Reference Home

The text of the 86Duino reference is a modification of the Arduino reference and is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.

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