Modbus Function Codes for Discrete Coils/Inputs

Functions
int8_t	Modbus::process_FC1 (uint16_t *regs, uint8_t u8size)
	This method processes functions 1 & 2 This method reads a bit array and transfers it to the master.
int8_t	Modbus::process_FC15 (uint16_t *regs, uint8_t u8size)
	This method processes function 15 This method writes a bit array assigned by the master.
int8_t	Modbus::process_FC5 (uint16_t *regs, uint8_t u8size)
	This method processes function 5 This method writes a value assigned by the master to a single bit.

Detailed Description

Function Documentation

process_FC1()

int8_t Modbus::process_FC1 ( uint16_t * regs, uint8_t u8size )

private

This method processes functions 1 & 2 This method reads a bit array and transfers it to the master.

Returns

u8BufferSize Response to master length

Definition at line 1302 of file ModbusRtu.h.

{
    uint8_t u8currentRegister, u8currentBit, u8bytesno, u8bitsno;
    uint8_t u8CopyBufferSize;
    uint16_t u16currentCoil, u16coil;
 
    // get the first and last coil from the message
    uint16_t u16StartCoil = word(au8Buffer[ADD_HI], au8Buffer[ADD_LO]);
    uint16_t u16Coilno = word(au8Buffer[NB_HI], au8Buffer[NB_LO]);
 
    // put the number of bytes in the outcoming message
    u8bytesno = (uint8_t)(u16Coilno / 8);
    if (u16Coilno % 8 != 0)
        u8bytesno++;
    au8Buffer[ADD_HI] = u8bytesno;
    u8BufferSize = ADD_LO;
 
    // read each coil from the register map and put its value inside the outcoming message
    u8bitsno = 0;
 
    for (u16currentCoil = 0; u16currentCoil < u16Coilno; u16currentCoil++)
    {
        u16coil = u16StartCoil + u16currentCoil;
        u8currentRegister = (uint8_t)(u16coil / 16);
        u8currentBit = (uint8_t)(u16coil % 16);
 
        bitWrite(
            au8Buffer[u8BufferSize],
            u8bitsno,
            bitRead(regs[u8currentRegister], u8currentBit));
        u8bitsno++;
 
        if (u8bitsno > 7)
        {
            u8bitsno = 0;
            u8BufferSize++;
        }
    }
 
    // send outcoming message
    if (u16Coilno % 8 != 0)
        u8BufferSize++;
    u8CopyBufferSize = u8BufferSize + 2;
    sendTxBuffer();
    return u8CopyBufferSize;
}

process_FC15()

int8_t Modbus::process_FC15 ( uint16_t * regs, uint8_t u8size )

private

This method processes function 15 This method writes a bit array assigned by the master.

Returns

u8BufferSize Response to master length

Definition at line 1447 of file ModbusRtu.h.

{
    uint8_t u8currentRegister, u8currentBit, u8frameByte, u8bitsno;
    uint8_t u8CopyBufferSize;
    uint16_t u16currentCoil, u16coil;
    boolean bTemp;
 
    // get the first and last coil from the message
    uint16_t u16StartCoil = word(au8Buffer[ADD_HI], au8Buffer[ADD_LO]);
    uint16_t u16Coilno = word(au8Buffer[NB_HI], au8Buffer[NB_LO]);
 
    // read each coil from the register map and put its value inside the outcoming message
    u8bitsno = 0;
    u8frameByte = 7;
    for (u16currentCoil = 0; u16currentCoil < u16Coilno; u16currentCoil++)
    {
 
        u16coil = u16StartCoil + u16currentCoil;
        u8currentRegister = (uint8_t)(u16coil / 16);
        u8currentBit = (uint8_t)(u16coil % 16);
 
        bTemp = bitRead(
            au8Buffer[u8frameByte],
            u8bitsno);
 
        bitWrite(
            regs[u8currentRegister],
            u8currentBit,
            bTemp);
 
        u8bitsno++;
 
        if (u8bitsno > 7)
        {
            u8bitsno = 0;
            u8frameByte++;
        }
    }
 
    // send outcoming message
    // it's just a copy of the incomping frame until 6th byte
    u8BufferSize = 6;
    u8CopyBufferSize = u8BufferSize + 2;
    sendTxBuffer();
    return u8CopyBufferSize;
}

process_FC5()

int8_t Modbus::process_FC5 ( uint16_t * regs, uint8_t u8size )

private

This method processes function 5 This method writes a value assigned by the master to a single bit.

Returns

u8BufferSize Response to master length

Definition at line 1389 of file ModbusRtu.h.

{
    uint8_t u8currentRegister, u8currentBit;
    uint8_t u8CopyBufferSize;
    uint16_t u16coil = word(au8Buffer[ADD_HI], au8Buffer[ADD_LO]);
 
    // point to the register and its bit
    u8currentRegister = (uint8_t)(u16coil / 16);
    u8currentBit = (uint8_t)(u16coil % 16);
 
    // write to coil
    bitWrite(
        regs[u8currentRegister],
        u8currentBit,
        au8Buffer[NB_HI] == 0xff);
 
    // send answer to master
    u8BufferSize = 6;
    u8CopyBufferSize = u8BufferSize + 2;
    sendTxBuffer();
 
    return u8CopyBufferSize;
}