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用vb做的modbus通信程序 怎麽沒有響應呢

Option?Explicit

Private?Sub?Form_Load()

MSComm1.InBufferCount?=?0

MSComm1.RThreshold?=?1

MSComm1.InputMode?=?comInputModeBinary

MSComm1.PortOpen?=?True

Text2?=?""

End?Sub

Private?Sub?Form_Unload(Cancel?As?Integer)

MSComm1.PortOpen?=?False

End?Sub

Private?Sub?MSComm1_OnComm()

Dim?input_buffer()?As?Byte

Dim?upper_limit?As?Long

Dim?input_to_hex?As?String

Dim?i?As?Integer

Select?Case?MSComm1.CommEvent

Case?comEvReceive

input_buffer?=?MSComm1.Input

upper_limit?=?UBound(input_buffer)

For?i?=?0?To?upper_limit

input_to_hex?=?Hex(input_buffer(i))

If?Len(input_to_hex)?<?2?Then

input_to_hex?=?"0"?&?input_to_hex

End?If

If?i?=?0?Then

Text2.Text?=?""

End?If

Text2.Text?=?Text2.Text?&?input_to_hex?&?""

Next

End?Select

End?Sub

Private?Sub?Text1_KeyPress(KeyAscii?As?Integer)

If?KeyAscii?=?13?Then

MSComm1.Output?=?Text1.Text?&?Chr(13)?&?Chr(10)

Text1.Text?=?""

Text1.TabIndex?=?0

End?If

End?Sub

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