一直看到有些朋友在问ModBus主从站的通讯问题，今天抽空儿给大家发几篇。

事先申明，我是调用的主从站库，库本身并不是我编写的，我没有那么大的能耐。

另外，上位机是用VB编写，VB本身不是很熟，如果有什么错误，请大家海谅。

最后，这仅仅只是一个测试程序，如果各位想用到商业方面，还需要各位自己去完善。

说明：PLC从站，PC作主站，用ModBus协议进行通讯。PC机读取PLCVW区的数据；PC机还读取PLC内部I或者O地址的状态。

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以下是PLC程序实现，方便贴出，已转换为STL

TITLE=程序注释

Network 1 // 网络标题

// 在第一个循环周期内初始化Modbus从站协议

LD SM0.1

CALL SBR3, 1, 12, 9600, 0, 0, 128, 32, 1000, &VB0, M10.1, MB11

Network 2

// 在每个循环周期内执行Modbus 从站协议

LD SM0.0

CALL SBR1, M10.2, MB12

Network 3

LD SM0.0

MOVW AIW0, VW100

/I +54, VW100

MOVW AIW2, VW102

/I +54, VW102

MOVW AIW4, VW104

/I +54, VW104

MOVW AIW6, VW106

/I +54, VW106

Network 4

LD SM0.0

= Q0.0

Network 5

LD I0.0

= Q0.1

Network 6

LD I0.1

= Q0.2

///////////////////////////////////

以下是VB源码

Option Explicit

PrivateｄｅｃｌａｒｅFunction GetTickco u* nt Lib "kernel32" () As Long

Dim x1

Dim p11, p12, p13, p14, p15, p16, p17, p18

Function CRC16(data() As Byte) As String

Dim CRC16Lo As Byte, CRC16Hi As Byte ‘CRC寄存器

Dim CL As Byte, CH As Byte ‘多项式码&HA001

Dim SaveHi As Byte, SaveLo As Byte

Dim i As Integer

Dim Flag As Integer

CRC16Lo = &HFF

CRC16Hi = &HFF

CL = &H1

CH = &HA0

For i = 0 To UBound(data)

CRC16Lo = CRC16Lo Xor data(i) ‘每一个数据与CRC寄存器进行异或

For Flag = 0 To 7

SaveHi = CRC16Hi

SaveLo = CRC16Lo

CRC16Hi = CRC16Hi \ 2 ‘高位右移一位

CRC16Lo = CRC16Lo \ 2 ‘低位右移一位

If ((SaveHi And &H1) = &H1) Then ‘如果高位字节最后一位为1

CRC16Lo = CRC16Lo Or &H80 ‘则低位字节右移后前面补1

End If ‘否则自动补0

If ((SaveLo And &H1) = &H1) Then ‘如果LSB为1，则与多项式码进行异或

CRC16Hi = CRC16Hi Xor CH

CRC16Lo = CRC16Lo Xor CL

End If

Next Flag

Next i

Dim ReturnData(1) As Byte

ReturnData(0) = CRC16Hi ‘CRC高位

ReturnData(1) = CRC16Lo ‘CRC低位

CRC16 = ReturnData

End Function

Private Sub About_Click()

frmAbout.Show

End Sub

Private Sub Form_Load() ‘初始化

Timer1.Enabled = False ‘定时器1无效

Timer1.Interval = 1000 ‘定时器1时间为1S

Timer2.Enabled = True ‘定时器2有效

Timer2.Interval = 1000 ‘定时器2时间为1S

Text1.Text = ""

Text2.Text = ""

Text3.Text = ""

Text4.Text = ""

Text5.Text = ""

Text6.Text = ""

Text8.Text = ""

Text10.Text = ""

MSComm1.CommPort = 1 ‘设定端口号

MSComm1.Settings = "9600,n,8,1" ‘设定通讯波特率

MSComm1.InBufferSize = 1024 ‘接收缓冲器大小

MSComm1.OutBufferSize = 1024 ‘输出缓冲器大小

MSComm1.InputMode = comInputModeBinary ‘以二进制传输

MSComm1.RThreshold = 1 ‘

MSComm1.SThreshold = 0

MSComm1.InputLen = 0 ‘读取接收缓冲器所有字符

MSComm1.OutBufferco u* nt = 0 ‘清空发送缓冲区

MSComm1.InBufferco u* nt = 0 ‘清空接收缓冲区

If MSComm1.PortOpen = False Then

Command3.Caption = "打开串口"

Else

Command3.Caption = "关闭串口"

End If

End Sub

Private Sub Command1_Click()

Timer1.Enabled = True

End Sub

Private Sub Command2_Click() ‘退出程序，定时器1无效

Timer1.Enabled = False

Cls

Unload Me

End Sub

Private Sub Command3_Click()

On Error Resume Next

If MSComm1.PortOpen = False Then

MSComm1.PortOpen = True

Else

MSComm1.PortOpen = False

End If

If MSComm1.PortOpen Then ‘打开关闭按钮显示文字

Command3.Caption = "关闭串口"

Else

Command3.Caption = "打开串口"

End If

If Err Then ‘打开串口失败，则显示出错信息

MsgBox Error$, 48, "错误信息"

Exit Sub

End If

End Sub

Private Sub Timer1_Timer() ‘读V存储区数据

Dim CRC() As Byte

Dim FGetData As String

Dim aa() As Byte

Dim s As String

Dim str As String

Dim i As Integer

Dim bb, cc As String

ReDim aa(5) As Byte ‘定义动态数组

aa(0) = &HC

aa(1) = &H3

aa(2) = &H0

aa(3) = &H32

aa(4) = &H0

aa(5) = &H4

CRC = CRC16(aa)

str = CRC

s = ""

For i = 1 To LenB(str)

s = s + Hex(AscB(m i* dB(str, i, 1)))

Next i

bb = Right(s, 2)

cc = m i* d(s, 1, 2)

If Len(s) < 4 Then

cc = m i* d(s, 1, 1)

End If

ReDim Preserve aa(0 To 7) As Byte

aa(6) = Val("&H" & bb)

aa(7) = Val("&H" & cc)

MSComm1.OutBufferco u* nt = 0 ‘清空输出寄存器

MSComm1.Output = aa

FGetData = ReceiveData

Text5.Text = FGetData

p11 = Val("&H" & m i* d(FGetData, 7, 4))

p12 = Val("&H" & m i* d(FGetData, 11, 4))

p13 = Val("&H" & m i* d(FGetData, 15, 4))

p14 = Val("&H" & m i* d(FGetData, 19, 4))

End Sub

Private Sub Command4_Click() ‘I状态

Dim CRC() As Byte

Dim FGetData As String

Dim aa() As Byte

Dim s As String

Dim str As String

Dim i As Integer

Dim bb, cc As String

ReDim aa(5) As Byte ‘定义动态数组

aa(0) = &HC

aa(1) = &H2

aa(2) = &H0

aa(3) = &H0

aa(4) = &H0

aa(5) = &H1

CRC = CRC16(aa)

str = CRC

s = ""

For i = 1 To LenB(str)

s = s + Hex(AscB(m i* dB(str, i, 1)))

Next i

bb = Right(s, 2)

cc = m i* d(s, 1, 2)

If Len(s) < 4 Then

cc = m i* d(s, 1, 1)

End If

ReDim Preserve aa(0 To 7) As Byte

aa(6) = Val("&H" & bb)

aa(7) = Val("&H" & cc)

MSComm1.OutBufferco u* nt = 0 ‘清空输出寄存器

MSComm1.Output = aa

FGetData = IReceiveData

p17 = Val("&H" & m i* d(FGetData, 7, 2))

p18 = Val("&H" & m i* d(FGetData, 9, 2))

End Sub

Private Sub Command5_Click() ‘Q状态

Dim CRC() As Byte

Dim FGetData As String

Dim aa() As Byte

Dim s As String

Dim str As String

Dim i As Integer

Dim bb, cc As String

ReDim aa(5) As Byte ‘定义动态数组

aa(0) = &HC

aa(1) = &H1

aa(2) = &H0

aa(3) = &H0

aa(4) = &H0

aa(5) = &H1

CRC = CRC16(aa)

str = CRC

s = ""

For i = 1 To LenB(str)

s = s + Hex(AscB(m i* dB(str, i, 1)))

Next i

bb = Right(s, 2)