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Basic Principles of Serial Data Transmission
2-26
Point-to-point connection CP 440 Installation and Parameter Assignment
A5E00057742-02
Sending Data with 3964(R)
The figure below illustrates the transmission sequence when data is sent with the
3964(R) procedure.
CP 440
Communication partner
User
data
Connection
cleardown
STX
DLE
1st byte
2nd byte
nth byte
DLE
ETX
BCC
DLE
Start code (02H)
Pos. acknowledgment (10H)
1st data byte
2nd data byte
nth data byte
End code (10H)
End code (03H)
3964(R) only
Pos. acknowledgment (10H)
Connection
setup
Figure 2-13
Data Traffic when Sending with the 3964(R) Procedure
Establishing a Send Connection
To establish the connection, the 3964(R) procedure sends the control code STX. If
the communication partner responds with the DLE code before the
acknowledgment delay time (ADT) expires, the procedure switches to send mode.
If the communication partner answers with NAK or with any other control code
(except for DLE or STX), or the acknowledgment delay time expires without a
response, the procedure repeats the connection setup. After the parameterized
number of unsuccessful setup attempts, the procedure aborts the connection setup
and sends the NAK code to the communication partner. The CP 440 reports the
error to the SEND_440 function block (STATUS output parameter).