freeModbus从buffer取出数据实例源码问题[已解决]

发布于 2019-02-19 17:29:40 浏览：2388 订阅该版

* 本帖最后由 lissettecarlr 于 2019-2-20 10:19 编辑 *

你好:在组件例程中port/user_mb_app_m.c文件中有如下函数，应该是通过他将从设备读出的数据保持的buffer中，我在主函数中也准备调用该函数来读出buffer中的数据，然后发现，函数中有一句eMode = MB_REG_WRITE;，这样该函数就没定死只能写入，下面的switch就没有意义了额，为什么会这么写呢，上面的注释是不是表明这语句是应该包含到if里面的呢？
原代码链接: [GITHUB](https://github.com/armink/FreeModbus_Slave-Master-RTT-STM32/blob/master/FreeModbus/port/user_mb_app_m.c)
```eMBErrorCode eMBMasterRegHoldingCB(UCHAR * pucRegBuffer, USHORT usAddress,
        USHORT usNRegs, eMBRegisterMode eMode)
{
    eMBErrorCode    eStatus = MB_ENOERR;
    USHORT          iRegIndex;
    USHORT *        pusRegHoldingBuf;
    USHORT          REG_HOLDING_START;
    USHORT          REG_HOLDING_NREGS;
    USHORT          usRegHoldStart;

pusRegHoldingBuf = usMRegHoldBuf[ucMBMasterGetDestAddress() - 1];
    REG_HOLDING_START = M_REG_HOLDING_START;
    REG_HOLDING_NREGS = M_REG_HOLDING_NREGS;
    usRegHoldStart = usMRegHoldStart;
    /* if mode is read, the master will write the received date to buffer. */
    eMode = MB_REG_WRITE;

/* it already plus one in modbus function method. */
    usAddress--;

if ((usAddress >= REG_HOLDING_START)
            && (usAddress + usNRegs <= REG_HOLDING_START + REG_HOLDING_NREGS))
    {
        iRegIndex = usAddress - usRegHoldStart;
        switch (eMode)
        {
        /* read current register values from the protocol stack. */
        case MB_REG_READ:
            while (usNRegs > 0)
            {
                *pucRegBuffer++ = (UCHAR) (pusRegHoldingBuf[iRegIndex] >> 8);
                *pucRegBuffer++ = (UCHAR) (pusRegHoldingBuf[iRegIndex] & 0xFF);
                iRegIndex++;
                usNRegs--;
            }
            break;
        /* write current register values with new values from the protocol stack. */
        case MB_REG_WRITE:
            while (usNRegs > 0)
            {
                pusRegHoldingBuf[iRegIndex] = *pucRegBuffer++ << 8;
                pusRegHoldingBuf[iRegIndex] |= *pucRegBuffer++;
                iRegIndex++;
                usNRegs--;
            }
            break;
        }
    }
    else
    {
        eStatus = MB_ENOREG;
    }
    return eStatus;
}```