Athena C10 line Manual de Instruções descarregar pdf (Página 10)

2.4.2 Visual Basic Calculate CRC16 example

Function CRC16(String As String) As String

Dim N As Integer, i As Integer, NByte As Integer

Dim CRC As Long, a As Byte

Dim Buffer As String

NByte = Len(String)

CRC = 65535

For i = 1 To NByte

a = Asc(Mid$(String, i, 1)) 'C(I)

CRC = (CRC Xor a) And &HFFFF

For N = 0 To 7

If CRC And 1 Then

CRC = (CRC \ 2)

CRC = (CRC Xor 40961)

Else

CRC = CRC \ 2

End If

Buffer = Right$("0000" + Hex$(CRC And &HFFFF), 4)

CRC16 = Chr$("&H" + Right$(Buffer, 2)) + Chr$("&H" + Left$(Buffer, 2))

End Function

2.5 Message Synchronisation

Message synchronisation between the transmitter and the receiver is

obtained by inserting a pause of at least 3.5 times the time of one

character between the messages. If the receiving device does not

receive for the time required for 3 characters, it considers the previous

message completed and concludes that the next byte received will be the

first of a new message and, consequently, an address.

3. The MODBUS Functions

This section provides a detailed description of the MODBUS functions

implemented on ATHENA CONTROLS instruments.

3.1 Read Output Status (01)

This function is used for requesting the ON or OFF status of binary

logical variables. Broadcast mode is not allowed.

Question

In addition to the address of the slave and the function code (01), the

message contains the starting address expressed in two bytes and the

number of bits to be read, also occupying two bytes. Address numbering

starts from zero (bit1 = 0) for MODBUS, or one (bit1 = 1) for JBUS.

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 106 107

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Athena C10 line Manual de Instruções Página 10