mbfunccoils.c主要是对线圈的一些描述。当主机接收到01、05、0F等功能码时，会进入对应功能码处理函数。

/* ----------------------- System includes ----------------------------------*/
#include "stdlib.h"
#include "string.h"

/* ----------------------- Platform includes --------------------------------*/
#include "port.h"

/* ----------------------- Modbus includes ----------------------------------*/
#include "mb.h"
#include "mbframe.h"
#include "mbproto.h"
#include "mbconfig.h"

/* ----------------------- Defines ------------------------------------------*/
#define MB_PDU_FUNC_READ_ADDR_OFF           ( MB_PDU_DATA_OFF )
#define MB_PDU_FUNC_READ_COILCNT_OFF        ( MB_PDU_DATA_OFF + 2 )
#define MB_PDU_FUNC_READ_SIZE               ( 4 )
#define MB_PDU_FUNC_READ_COILCNT_MAX        ( 0x07D0 )

#define MB_PDU_FUNC_WRITE_ADDR_OFF          ( MB_PDU_DATA_OFF )
#define MB_PDU_FUNC_WRITE_VALUE_OFF         ( MB_PDU_DATA_OFF + 2 )
#define MB_PDU_FUNC_WRITE_SIZE              ( 4 )

#define MB_PDU_FUNC_WRITE_MUL_ADDR_OFF      ( MB_PDU_DATA_OFF )
#define MB_PDU_FUNC_WRITE_MUL_COILCNT_OFF   ( MB_PDU_DATA_OFF + 2 )
#define MB_PDU_FUNC_WRITE_MUL_BYTECNT_OFF   ( MB_PDU_DATA_OFF + 4 )
#define MB_PDU_FUNC_WRITE_MUL_VALUES_OFF    ( MB_PDU_DATA_OFF + 5 )
#define MB_PDU_FUNC_WRITE_MUL_SIZE_MIN      ( 5 )
#define MB_PDU_FUNC_WRITE_MUL_COILCNT_MAX   ( 0x07B0 )

/* ----------------------- Static functions ---------------------------------*/
eMBException    prveMBError2Exception( eMBErrorCode eErrorCode );

/* ----------------------- Start implementation -----------------------------*/
/*
Function Code：01，读线圈状态
发送：1丛机地址+1功能码+2起始地址+2线圈数量+2CRC
返回：1丛机地址+1功能码+1字节数+2线圈状态+2CRC
*/
#if MB_FUNC_READ_COILS_ENABLED > 0
eMBException
eMBFuncReadCoils( UCHAR * pucFrame, USHORT * usLen )    
{
    USHORT          usRegAddress;
    USHORT          usCoilCount;
    UCHAR           ucNBytes;
    UCHAR          *pucFrameCur;

    eMBException    eStatus = MB_EX_NONE;
    eMBErrorCode    eRegStatus;

    /* 校验PDU长度是否合理 */
    if( *usLen == ( MB_PDU_FUNC_READ_SIZE + MB_PDU_SIZE_MIN ) ) //1+4
    {
        /* 线圈地址 */
        usRegAddress = ( USHORT )( pucFrame[MB_PDU_FUNC_READ_ADDR_OFF] << 8 );
        usRegAddress |= ( USHORT )( pucFrame[MB_PDU_FUNC_READ_ADDR_OFF + 1] );
        /* 第1个线圈寻址为0，所以地址加一 */
        usRegAddress++;

        /* 线圈数量 */
        usCoilCount = ( USHORT )( pucFrame[MB_PDU_FUNC_READ_COILCNT_OFF] << 8 );
        usCoilCount |= ( USHORT )( pucFrame[MB_PDU_FUNC_READ_COILCNT_OFF + 1] );

        if( ( usCoilCount >= 1 ) && ( usCoilCount < MB_PDU_FUNC_READ_COILCNT_MAX ) )    /* 检查线圈数量是否合理，1~2000 */
        {
            pucFrameCur = &pucFrame[MB_PDU_FUNC_OFF];   //pucFrameCur指向pucFrame数组的开头
            *usLen = MB_PDU_FUNC_OFF;                   //长度初始值0

            *pucFrameCur++ = MB_FUNC_READ_COILS;        //加入功能码
            *usLen += 1;                                //长度为1

            if( ( usCoilCount & 0x0007 ) != 0 )         //是否被8整除
            {
                ucNBytes = ( UCHAR )( usCoilCount / 8 + 1 );
            }
            else
            {
                ucNBytes = ( UCHAR )( usCoilCount / 8 );
            }
            *pucFrameCur++ = ucNBytes;                  //加入用到的字节数
            *usLen += 1;                                //长度为2

            eRegStatus = eMBRegCoilsCB( pucFrameCur, usRegAddress, usCoilCount, MB_REG_READ );

            if( eRegStatus != MB_ENOERR )
            {
                eStatus = prveMBError2Exception( eRegStatus );
            }
            else
            {
                *usLen += ucNBytes;
            }
        }
        else
        {
            eStatus = MB_EX_ILLEGAL_DATA_VALUE;
        }
    }
    else
    {
        eStatus = MB_EX_ILLEGAL_DATA_VALUE;
    }
    return eStatus;
}
#endif

/*
Function Code：05，写单个线圈
发送：1丛机地址+1功能码+2起始地址+2线圈状态+2CRC
返回：1丛机地址+1功能码+2起始地址+2线圈状态+2CRC
线圈状态：0xFF00-ON，0x0000-OFF
*/
#if MB_FUNC_WRITE_COIL_ENABLED > 0
eMBException
eMBFuncWriteCoil( UCHAR * pucFrame, USHORT * usLen )    
{
    USHORT          usRegAddress;
    UCHAR           ucBuf[1];

    eMBException    eStatus = MB_EX_NONE;
    eMBErrorCode    eRegStatus;

    if( *usLen == ( MB_PDU_FUNC_WRITE_SIZE + MB_PDU_SIZE_MIN ) )    //1+4
    {
        usRegAddress = ( USHORT )( pucFrame[MB_PDU_FUNC_WRITE_ADDR_OFF] << 8 );
        usRegAddress |= ( USHORT )( pucFrame[MB_PDU_FUNC_WRITE_ADDR_OFF + 1] );
        usRegAddress++;

        if( ( pucFrame[MB_PDU_FUNC_WRITE_VALUE_OFF + 1] == 0x00 ) &&
            ( ( pucFrame[MB_PDU_FUNC_WRITE_VALUE_OFF] == 0xFF ) || ( pucFrame[MB_PDU_FUNC_WRITE_VALUE_OFF] == 0x00 ) ) )
        {
            if( pucFrame[MB_PDU_FUNC_WRITE_VALUE_OFF] == 0xFF )
            {
                ucBuf[0] = 1;
            }
            else
            {
                ucBuf[0] = 0;
            }
            eRegStatus = eMBRegCoilsCB( &ucBuf[0], usRegAddress, 1, MB_REG_WRITE );

            if( eRegStatus != MB_ENOERR )
            {
                eStatus = prveMBError2Exception( eRegStatus );
            }
        }
        else
        {
            eStatus = MB_EX_ILLEGAL_DATA_VALUE;
        }
    }
    else
    {
        eStatus = MB_EX_ILLEGAL_DATA_VALUE;
    }
    return eStatus;
}

/*
Function Code：0F，写多个线圈
发送：1丛机地址+1功能码+2起始地址+2线圈数量+1字节数+2字节线圈状态+2CRC
返回：1丛机地址+1功能码+2起始地址+2线圈状态+2CRC
*/
#if MB_FUNC_WRITE_MULTIPLE_COILS_ENABLED > 0
eMBException
eMBFuncWriteMultipleCoils( UCHAR * pucFrame, USHORT * usLen )   
{
    USHORT          usRegAddress;       
    USHORT          usCoilCnt;          
    UCHAR           ucByteCount;        
    UCHAR           ucByteCountVerify;

    eMBException    eStatus = MB_EX_NONE;
    eMBErrorCode    eRegStatus;

    if( *usLen > ( MB_PDU_SIZE_MIN + MB_PDU_FUNC_WRITE_SIZE ) )     //1+4
    {   
        usRegAddress = ( USHORT )( pucFrame[MB_PDU_FUNC_WRITE_MUL_ADDR_OFF] << 8 );     
        usRegAddress |= ( USHORT )( pucFrame[MB_PDU_FUNC_WRITE_MUL_ADDR_OFF + 1] );     
        usRegAddress++;

        usCoilCnt = ( USHORT )( pucFrame[MB_PDU_FUNC_WRITE_MUL_COILCNT_OFF] << 8 );    
        usCoilCnt |= ( USHORT )( pucFrame[MB_PDU_FUNC_WRITE_MUL_COILCNT_OFF + 1] );     

        ucByteCount = pucFrame[MB_PDU_FUNC_WRITE_MUL_BYTECNT_OFF];     

        if( ( usCoilCnt & 0x0007 ) != 0 )
        {
            ucByteCountVerify = ( UCHAR )( usCoilCnt / 8 + 1 );
        }
        else
        {
            ucByteCountVerify = ( UCHAR )( usCoilCnt / 8 );
        }

        if( ( usCoilCnt >= 1 ) && ( usCoilCnt <= MB_PDU_FUNC_WRITE_MUL_COILCNT_MAX ) && ( ucByteCountVerify == ucByteCount ) )
        {
            eRegStatus = eMBRegCoilsCB( &pucFrame[MB_PDU_FUNC_WRITE_MUL_VALUES_OFF], usRegAddress, usCoilCnt, MB_REG_WRITE );

            if( eRegStatus != MB_ENOERR )
            {
                eStatus = prveMBError2Exception( eRegStatus );
            }
            else
            {
                *usLen = MB_PDU_FUNC_WRITE_MUL_BYTECNT_OFF;
            }
        }
        else
        {
            eStatus = MB_EX_ILLEGAL_DATA_VALUE;
        }
    }
    else
    {
        /* Can't be a valid write coil register request because the length
         * is incorrect. */
        eStatus = MB_EX_ILLEGAL_DATA_VALUE;
    }
    return eStatus;
}
#endif
#endif