freemodbus-v1.5.0 源码分析 (转)
分类:
IT文章
•
2022-07-29 09:58:37
FreeModbus协议栈作为从机，等待主机传送的数据，当从机接收到一帧完整的报文后，对报文进行解析，然后响应主机，发送报文给主机，实现主机和从机之间的通信。
1、初始化协议栈---eMBInit函数（mb.c中），以RTU为例
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1 eMBErrorCode eMBInit( eMBMode eMode, UCHAR ucSlaveAddress, UCHAR ucPort, ULONG ulBaudRate, eMBParity eParity )
2 {
3
4 ?1/*函数功能：*1:实现RTU模式和ASCALL模式的协议栈初始化;*2:完成协议栈核心函数指针的赋值，包括Modbus协议栈的使能和禁止、报文的接收和响应、3.5T定时器中断回调函数、串口发送和接收中断回调函数;*3:eMBRTUInit完成RTU模式下串口和3.5T定时器的初始化，需用户自己移植;*4:设置Modbus协议栈的模式eMBCurrentMode为MB_RTU，设置Modbus协议栈状态eMBState为STATE_DISABLED;*/ eMBErrorCode eStatus = MB_ENOERR;
5 /* check preconditions */
6 if( ( ucSlaveAddress == MB_ADDRESS_BROADCAST ) ||
7 ( ucSlaveAddress < MB_ADDRESS_MIN ) || ( ucSlaveAddress > MB_ADDRESS_MAX ) ) //验证从机地址
8 {
9 eStatus = MB_EINVAL; //地址错误
10 }
11 else
12 {
13 ucMBAddress = ucSlaveAddress;
14
15 switch ( eMode )
16 {
17 #if MB_RTU_ENABLED > 0
18 case MB_RTU:
19 pvMBFrameStartCur = eMBRTUStart;
20 pvMBFrameStopCur = eMBRTUStop;
21 peMBFrameSendCur = eMBRTUSend;
22 peMBFrameReceiveCur = eMBRTUReceive;
23 pvMBFrameCloseCur = MB_PORT_HAS_CLOSE ? vMBPortClose : NULL;
24 pxMBFrameCBByteReceived = xMBRTUReceiveFSM; //接收状态机，串口接受中断最终调用此函数接收数据
25 pxMBFrameCBTransmitterEmpty = xMBRTUTransmitFSM; //发送状态机，串口发送中断最终调用此函数发送数据
26 pxMBPortCBTimerExpired = xMBRTUTimerT35Expired; //报文到达间隔检查，定时器中断函数最终调用次函数完成定时器中断
27
28 eStatus = eMBRTUInit( ucMBAddress, ucPort, ulBaudRate, eParity );
29 break;
30 #endif
31 #if MB_ASCII_ENABLED > 0
32 case MB_ASCII:
33 pvMBFrameStartCur = eMBASCIIStart;
34 pvMBFrameStopCur = eMBASCIIStop;
35 peMBFrameSendCur = eMBASCIISend;
36 peMBFrameReceiveCur = eMBASCIIReceive;
37 pvMBFrameCloseCur = MB_PORT_HAS_CLOSE ? vMBPortClose : NULL;
38 pxMBFrameCBByteReceived = xMBASCIIReceiveFSM;
39 pxMBFrameCBTransmitterEmpty = xMBASCIITransmitFSM;
40 pxMBPortCBTimerExpired = xMBASCIITimerT1SExpired;
41
42 eStatus = eMBASCIIInit( ucMBAddress, ucPort, ulBaudRate, eParity );
43 break;
44 #endif
45 default:
46 eStatus = MB_EINVAL;
47 }
48
49 if( eStatus == MB_ENOERR )
50 {
51 if( !xMBPortEventInit( ) )
52 {
53 /* port dependent event module initalization failed. */
54 eStatus = MB_EPORTERR;
55 }
56 else
57 {//设定当前状态
58 eMBCurrentMode = eMode; //设定RTU模式
59 eMBState = STATE_DISABLED; //modbus协议栈初始化状态,在此初始化为禁止
60 }
61 }
62 }
63 return eStatus;
64 }
View Code
eMBInit函数中pvMBFrameStartCur、pvMBFrameStartCur等为协议栈函数的接口，对于不同的通信模式使用不同的函数进行初始化！！！此编程模式可以借鉴学习！！！
eMBInit函数对底层驱动（串口和定时器）进行初始化。初始化完成并且成功之后对事件也进行了初始化，完成后全局变量eMBState=STATE_DISABLED。
2、启动协议栈----eMBEnable函数（mb.c函数）
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1 eMBErrorCode
2 eMBEnable( void )
3 {
4 /*函数功能：
5 *1:实现RTU模式和ASCALL模式的协议栈初始化;
6 *2:完成协议栈核心函数指针的赋值，包括Modbus协议栈的使能和禁止、报文的接收和响应、3.5T定时器中断回调函数、串口发送和接收中断回调函数;
7 *3:eMBRTUInit完成RTU模式下串口和3.5T定时器的初始化，需用户自己移植;
8 *4:设置Modbus协议栈的模式eMBCurrentMode为MB_RTU，设置Modbus协议栈状态eMBState为STATE_DISABLED;
9 */
10 eMBErrorCode eStatus = MB_ENOERR;
11
12 if( eMBState == STATE_DISABLED )
13 {
14 /* Activate the protocol stack. */
15 pvMBFrameStartCur( ); //激活协议栈
16 eMBState = STATE_ENABLED; //设置Modbus协议栈工作状态eMBState为STATE_ENABLED
17 }
18 else
19 {
20 eStatus = MB_EILLSTATE;
21 }
22 return eStatus;
23 }
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---eMBRTUStart函数 （mbrtu.c）
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1 void
2 eMBRTUStart( void )
3 {
4 /*函数功能
5 * 1:设置接收状态机eRcvState为STATE_RX_INIT；
6 * 2:使能串口接收,禁止串口发送,作为从机,等待主机传送的数据;
7 * 3:开启定时器，3.5T时间后定时器发生第一次中断,此时eRcvState为STATE_RX_INIT,上报初始化完成事件,然后设置eRcvState为空闲STATE_RX_IDLE;
8 * 4:每次进入3.5T定时器中断,定时器被禁止，等待串口有字节接收后，才使能定时器;
9 * */
10 ENTER_CRITICAL_SECTION( );
11 /* Initially the receiver is in the state STATE_RX_INIT. we start
12 * the timer and if no character is received within t3.5 we change
13 * to STATE_RX_IDLE. This makes sure that we delay startup of the
14 * modbus protocol stack until the bus is free.
15 */
16 eRcvState = STATE_RX_INIT;
17 vMBPortSerialEnable( TRUE, FALSE ); //开启串口接收，发送未开启
18 vMBPortTimersEnable( ); //启动定时器
19
20 EXIT_CRITICAL_SECTION( );
21 }
View Code
eMBEnable函数启动协议栈pvMBFrameStartCur，对于RTU模式，pvMBFrameStartCur函数指针指向 eMBRTUStart，在eMBRTUStart函数中，全局变量eRcvState=STATE_RX_INIT,并使能串口和定时器。注意！！！此时定时器将开始工作！！！。eMBEnable函数中将把全局变量改为 eMBState=STATE_ENABLED。
3、状态机轮训---eMBPoll函数（mb.c）
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1 eMBErrorCode eMBPoll( void )
2 {
3 /*函数功能:
4 *1:检查协议栈状态是否使能，eMBState初值为STATE_NOT_INITIALIZED，在eMBInit()函数中被赋值为STATE_DISABLED,在eMBEnable函数中被赋值为STATE_ENABLE;
5 *2:轮询EV_FRAME_RECEIVED事件发生，若EV_FRAME_RECEIVED事件发生，接收一帧报文数据，上报EV_EXECUTE事件，解析一帧报文，响应(发送)一帧数据给主机;
6 */
7 static UCHAR *ucMBFrame; //接收和发送报文数据缓存区
8 static UCHAR ucRcvAddress; //modbus从机地址
9 static UCHAR ucFunctionCode; //功能码
10 static USHORT usLength; //报文长度
11 static eMBException eException; //错误码响应 枚举
12
13 int i;
14 eMBErrorCode eStatus = MB_ENOERR;
15 eMBEventType eEvent; //错误码
16
17 /* Check if the protocol stack is ready. */
18 if( eMBState != STATE_ENABLED ) //检查协议栈是否使能
19 {
20 return MB_EILLSTATE; //协议栈未使能，返回协议栈无效错误码
21 }
22
23 /* Check if there is a event available. If not return control to caller.
24 * Otherwise we will handle the event. */
25
26 if( xMBPortEventGet( &eEvent ) == TRUE ) //判断事件是否发生
27 {
28 switch ( eEvent ) //查询哪个事件发生
29 {
30 case EV_READY:
31 break;
32
33 case EV_FRAME_RECEIVED: //接收到一帧数据，此事件发生
34 eStatus = peMBFrameReceiveCur( &ucRcvAddress, &ucMBFrame, &usLength ); //接收数据，并检验报文长度和CRC校验是否正确
35 /*
36 * ucRcvAddress 主站要读取的从站的地址
37 * ucMBFrame 指向PDU的头部
38 * usLength PDU的长度
39 */
40 if( eStatus == MB_ENOERR )
41 {
42 /* Check if the frame is for us. If not ignore the frame. */
43 if( ( ucRcvAddress == ucMBAddress ) || ( ucRcvAddress == MB_ADDRESS_BROADCAST ) )
44 {
45 ( void )xMBPortEventPost( EV_EXECUTE ); //修改事件标志为EV_EXECUTE执行事件
46 }
47 }
48 break;
49
50 case EV_EXECUTE: //修改事件标志为EV_EXECUTE执行事件
51 ucFunctionCode = ucMBFrame[MB_PDU_FUNC_OFF]; //提取功能码
52 eException = MB_EX_ILLEGAL_FUNCTION; //赋错误码初值为无效的功能码
53 for( i = 0; i < MB_FUNC_HANDLERS_MAX; i++ )
54 {
55 /* No more function handlers registered. Abort. */
56 if( xFuncHandlers[i].ucFunctionCode == 0 )
57 {
58 break;
59 }
60 else if( xFuncHandlers[i].ucFunctionCode == ucFunctionCode ) //根据报文中的功能码，处理报文
61 {
62 eException = xFuncHandlers[i].pxHandler( ucMBFrame, &usLength ); //对接收到的报文进行解析
63 break;
64 }
65 }
66
67 /* If the request was not sent to the broadcast address we
68 * return a reply. */
69 if( ucRcvAddress != MB_ADDRESS_BROADCAST )
70 {
71 if( eException != MB_EX_NONE ) //接收到的报文有错误
72 {
73 /* An exception occured. Build an error frame. */
74 usLength = 0; //响应发送数据的首字节为从机地址
75 ucMBFrame[usLength++] = ( UCHAR )( ucFunctionCode | MB_FUNC_ERROR ); //响应发送数据帧的第二个字节，功能码最高位置1
76 ucMBFrame[usLength++] = eException; //响应发送数据帧的第三个字节为错误码标识
77 }
78 if( ( eMBCurrentMode == MB_ASCII ) && MB_ASCII_TIMEOUT_WAIT_BEFORE_SEND_MS )
79 {
80 vMBPortTimersDelay( MB_ASCII_TIMEOUT_WAIT_BEFORE_SEND_MS );
81 }
82 eStatus = peMBFrameSendCur( ucMBAddress, ucMBFrame, usLength ); //modbus从机响应函数,发送响应给主机
83 }
84 break;
85
86 case EV_FRAME_SENT:
87 break;
88 }
89 }
90 return MB_ENOERR;
91 }
View Code
在eMBPoll函数中，首先由 xMBPortEventGet( &eEvent ) == TRUE 判断时间是否发生，若无事件发生则不进入状态机；若有时间发生则进入状态机开始轮询。状态机的时间转换在定时中断服务函数中实现。
在eMBEnable函数中启动定时器后，定时器开始工作（见 eMBRTUStart函数）， 在定时器第一次超时之后将会发送xNeedPoll = xMBPortEventPost( EV_READY ) 事件，然后关闭定时器，接收机状态（全局变量）eRcvState为STATE_RX_IDLE。此时，主循环eMBPoll中将执行一次EV_READY下的操作。至此，完成Modbus协议栈的初始化准备工作，协议栈开始运行，eMBPoll()函数轮询等待接收完成事件发生。
---定时器中断服务函数
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1 void BOARD_GPTA_HANDLER()
2 {
3 // BOOL bTaskWoken = FALSE;
4
5 PRINTF("
Timer Expired:
");
6 vMBPortSetWithinException( TRUE );
7 GPT_ClearStatusFlag(BOARD_GPTA_BASEADDR, gptStatusFlagOutputCompare1); //关闭定时器
8 ( void )pxMBPortCBTimerExpired( ); //事件转换 vMBPortSetWithinException( FALSE );
9 }
View Code
---xMBRTUTimerT35Expired T3.5超时函数
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1 BOOL xMBRTUTimerT35Expired( void )
2 {
3 /* 函数功能
4 * 1:从机接受完成一帧数据后，接收状态机eRcvState为STATE_RX_RCV；
5 * 2:上报“接收到报文”事件(EV_FRAME_RECEIVED);
6 * 3:禁止3.5T定时器，设置接收状态机eRcvState状态为STATE_RX_IDLE空闲;
7 */
8 BOOL xNeedPoll = FALSE;
9
10 switch ( eRcvState ) //上报modbus协议栈的事件状态给poll函数
11 {
12 /* Timer t35 expired. Startup phase is finished. */
13 case STATE_RX_INIT:
14 xNeedPoll = xMBPortEventPost( EV_READY ); //初始化完成事件
15 break;
16
17 /* A frame was received and t35 expired. Notify the listener that
18 * a new frame was received. */
19 case STATE_RX_RCV: //一帧数据接收完成
20 xNeedPoll = xMBPortEventPost( EV_FRAME_RECEIVED ); //上报协议栈事件,接收到一帧完整的数据
21 break;
22
23 /* An error occured while receiving the frame. */
24 case STATE_RX_ERROR:
25 break;
26
27 /* Function called in an illegal state. */
28 default:
29 assert( ( eRcvState == STATE_RX_INIT ) ||
30 ( eRcvState == STATE_RX_RCV ) || ( eRcvState == STATE_RX_ERROR ) );
31 }
32
33 vMBPortTimersDisable( ); //当接收到一帧数据后，禁止3.5T定时器，直到接受下一帧数据开始，开始计时
34 eRcvState = STATE_RX_IDLE; //处理完一帧数据，接收器状态为空闲
35
36 return xNeedPoll;
37 }
View Code
4、报文接收
在定时器第一次中断之后，状态机为eRcvState=STATE_RX_IDLE，即读空闲状态，eMBPoll也阻塞在等待接收完成事件发生。而在eMBPoll之前的eMBRTUStart函数中已经开启了串口中断，因此在接收到数据之后，串口中断将会响应，在串口中断服务函数中将调用接收状态机函数xMBRTUReceiveFSM来接收数据。
---xMBRTUReceiveFSM函数
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1 BOOL xMBRTUReceiveFSM( void )
2 {
3 /*函数功能
4 *1:将接收到的数据存入ucRTUBuf[]中;
5 *2:usRcvBufferPos为全局变量，表示接收数据的个数;
6 *3:每接收到一个字节的数据，3.5T定时器清0
7 */
8
9 BOOL xTaskNeedSwitch = FALSE;
10 UCHAR ucByte;
11
12 assert( eSndState == STATE_TX_IDLE ); //确保没有数据在发送
13
14 /* Always read the character. */
15 ( void )xMBPortSerialGetByte( ( CHAR * ) & ucByte ); //从串口数据寄存器读取一个字节数据
16
17 switch ( eRcvState ) //根据不同的状态转移
18 {
19 /* If we have received a character in the init state we have to
20 * wait until the frame is finished.
21 */
22 case STATE_RX_INIT:
23 vMBPortTimersEnable( ); //开启3.5T定时器
24 break;
25
26 /* In the error state we wait until all characters in the
27 * damaged frame are transmitted.
28 */
29 case STATE_RX_ERROR: //数据帧被损坏，重启定时器，不保存串口接收的数据
30 vMBPortTimersEnable( );
31 break;
32
33 /* In the idle state we wait for a new character. If a character
34 * is received the t1.5 and t3.5 timers are started and the
35 * receiver is in the state STATE_RX_RECEIVCE.
36 */
37 case STATE_RX_IDLE: // 接收器空闲，开始接收，进入STATE_RX_RCV状态
38 usRcvBufferPos = 0;
39 ucRTUBuf[usRcvBufferPos++] = ucByte; //保存数据
40 eRcvState = STATE_RX_RCV;
41
42 /* Enable t3.5 timers. */
43 vMBPortTimersEnable( ); //每收到一个字节，都重启3.5T定时器
44 break;
45
46 /* We are currently receiving a frame. Reset the timer after
47 * every character received. If more than the maximum possible
48 * number of bytes in a modbus frame is received the frame is
49 * ignored.
50 */
51 case STATE_RX_RCV:
52 if( usRcvBufferPos < MB_SER_PDU_SIZE_MAX )
53 {
54 ucRTUBuf[usRcvBufferPos++] = ucByte; //接收数据
55 }
56 else
57 {
58 eRcvState = STATE_RX_ERROR; //一帧报文的字节数大于最大PDU长度，忽略超出的数据
59 }
60 vMBPortTimersEnable( ); //每收到一个字节，都重启3.5T定时器
61 break;
62 }
63 return xTaskNeedSwitch;
64 }
View Code
在串口中断前，状态机为eRcvState=STATE_RX_IDLE，接收状态机开始后，读取uart串口缓存中的数据，并进入STATE_RX_IDLE分支中存储一次数据后开启定时器，然后进入STATE_RX_RCV分支继续接收后续的数据，直至定时器超时！如果没有超时的话，状态不会转换，将还可以继续接收数据。超时之后，在T3.5超时函数xMBRTUTimerT35Expired 中将发送EV_FRAME_RECEIVED事件。然后eMBPoll函数将会调用eMBRTUReceive函数。
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1 /* A frame was received and t35 expired. Notify the listener that
2 * a new frame was received. */
3 case STATE_RX_RCV: //一帧数据接收完成
4 xNeedPoll = xMBPortEventPost( EV_FRAME_RECEIVED ); //上报协议栈事件,接收到一帧完整的数据
5 break;
View Code
---eMBRTUReceive函数
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1 eMBErrorCode
2 eMBRTUReceive( UCHAR * pucRcvAddress, UCHAR ** pucFrame, USHORT * pusLength )
3 {
4 /*eMBPoll函数轮询到EV_FRAME_RECEIVED事件时,调用peMBFrameReceiveCur()，
5 * 此函数是用户为函数指针peMBFrameReceiveCur()的赋值,
6 * 此函数完成的功能：
7 * 从一帧数据报文中，取得modbus从机地址给pucRcvAddress、PDU报文的长度给pusLength，
8 * PDU报文的首地址给pucFrame，函数*形参全部为地址传递，
9 */
10 BOOL xFrameReceived = FALSE;
11 eMBErrorCode eStatus = MB_ENOERR;
12
13 ENTER_CRITICAL_SECTION( );
14 assert( usRcvBufferPos < MB_SER_PDU_SIZE_MAX ); //断言宏，判断接收到的字节数<256，如果>256，终止程序
15
16 /* Length and CRC check */
17 if( ( usRcvBufferPos >= MB_SER_PDU_SIZE_MIN )
18 && ( usMBCRC16( ( UCHAR * ) ucRTUBuf, usRcvBufferPos ) == 0 ) )
19 {
20 /* Save the address field. All frames are passed to the upper layed
21 * and the decision if a frame is used is done there.
22 */
23 *pucRcvAddress = ucRTUBuf[MB_SER_PDU_ADDR_OFF]; //保存从站地址
24
25 /* Total length of Modbus-PDU is Modbus-Serial-Line-PDU minus
26 * size of address field and CRC checksum.
27 */
28 *pusLength = ( USHORT )( usRcvBufferPos - MB_SER_PDU_PDU_OFF - MB_SER_PDU_SIZE_CRC ); //PDU长度
29
30 /* Return the start of the Modbus PDU to the caller. */
31 *pucFrame = ( UCHAR * ) & ucRTUBuf[MB_SER_PDU_PDU_OFF]; //pucFrame指向PDU起始位置
32 xFrameReceived = TRUE;
33 }
34 else
35 {
36 eStatus = MB_EIO;
37 }
38
39 EXIT_CRITICAL_SECTION( );
40 return eStatus;
41 }
View Code
eMBRTUReceive函数完成了CRC校验、帧数据地址和长度的赋值，便于给上层进行处理！之后eMBPoll函数发送 ( void )xMBPortEventPost( EV_EXECUTE )事件。在EV_EXECUTE 事件中，从站对接收到的数据进行处理，包括根据功能码寻找功能函数处理报文和调用eStatus = peMBFrameSendCur( ucMBAddress, ucMBFrame, usLength ) 发送应答报文。
--- eMBRTUSend函数
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1 eMBErrorCode eMBRTUSend( UCHAR ucSlaveAddress, const UCHAR * pucFrame, USHORT usLength )
2 {
3 /*函数功能
4 * 1:对响应报文PDU前面加上从机地址;
5 * 2:对响应报文PDU后加上CRC校;
6 * 3:使能发送，启动传输;*/
7 eMBErrorCode eStatus = MB_ENOERR;
8 USHORT usCRC16;
9
10 ENTER_CRITICAL_SECTION( );
11
12 /* Check if the receiver is still in idle state. If not we where to
13 * slow with processing the received frame and the master sent another
14 * frame on the network. We have to abort sending the frame.
15 */
16 if( eRcvState == STATE_RX_IDLE )
17 {
18 /* First byte before the Modbus-PDU is the slave address. */
19 pucSndBufferCur = ( UCHAR * ) pucFrame - 1; //在协议数据单元前加从机地址
20 usSndBufferCount = 1;
21
22 /* Now copy the Modbus-PDU into the Modbus-Serial-Line-PDU. */
23 pucSndBufferCur[MB_SER_PDU_ADDR_OFF] = ucSlaveAddress;
24 usSndBufferCount += usLength;
25
26 /* Calculate CRC16 checksum for Modbus-Serial-Line-PDU. */
27 usCRC16 = usMBCRC16( ( UCHAR * ) pucSndBufferCur, usSndBufferCount );
28 ucRTUBuf[usSndBufferCount++] = ( UCHAR )( usCRC16 & 0xFF );
29 ucRTUBuf[usSndBufferCount++] = ( UCHAR )( usCRC16 >> 8 );
30
31 /* Activate the transmitter. */
32 eSndState = STATE_TX_XMIT; //发送状态
33 //以下为新添加
34 xMBPortSerialPutByte( ( CHAR )*pucSndBufferCur ); //发送一个字节的数据，进入发送中断函数，启动传输
35 pucSndBufferCur++; /* next byte in sendbuffer. */
36 usSndBufferCount--;
37
38 vMBPortSerialEnable( FALSE, TRUE ); //使能发送，禁止接收
39 }
40 else
41 {
42 eStatus = MB_EIO;
43 }
44 EXIT_CRITICAL_SECTION( );
45 return eStatus;
46 }
View Code
在 eMBRTUSend函数中会调用串口发送数据，在进入串口发送中断后会调用xMBRTUTransmitFSM发送状态机函数发送应答报文。
---xMBRTUTransmitFSM函数
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1 BOOL xMBRTUTransmitFSM( void )
2 {
3 BOOL xNeedPoll = FALSE;
4
5 assert( eRcvState == STATE_RX_IDLE );
6
7 switch ( eSndState )
8 {
9 /* We should not get a transmitter event if the transmitter is in
10 * idle state. */
11 case STATE_TX_IDLE:
12 /* enable receiver/disable transmitter. */
13 vMBPortSerialEnable( TRUE, FALSE ); //发送器处于空闲状态，使能接收，禁止发送
14 break;
15
16 case STATE_TX_XMIT: //发送器处于发送状态,在从机发送函数eMBRTUSend中赋值STATE_TX_XMIT
17 /* check if we are finished. */
18 if( usSndBufferCount != 0 ) //发送数据
19 {
20 xMBPortSerialPutByte( ( CHAR )*pucSndBufferCur );
21 pucSndBufferCur++; /* next byte in sendbuffer. */
22 usSndBufferCount--;
23 }
24 else //传递任务，发送完成
25 {
26 xNeedPoll = xMBPortEventPost( EV_FRAME_SENT ); //协议栈事件状态赋值为EV_FRAME_SENT,发送完成事件,eMBPoll函数会对此事件进行处理
27 /* Disable transmitter. This prevents another transmit buffer
28 * empty interrupt. */
29 vMBPortSerialEnable( TRUE, FALSE ); //使能接收，禁止发送
30 eSndState = STATE_TX_IDLE; //发送器状态为空闲状态
31 }
32 break;
33 }
34
35 return xNeedPoll;
36 }
View Code
至此：协议栈准备工作，从机接受报文，解析报文，从机发送响应报文四部分结束。
原贴链接： http://www.cnblogs.com/wujing-hubei/p/5935142.html
参考：
freemodbus库函数详解 FreeModbus源码详解-程序设计
Freemodbus完全分析_百度文库
FreeModbus学习笔记_百度文库
