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Basic Principles of Serial Data Transmission
2.5 Data Transmission with the 3964(R) Procedure
Sending Data
If a connection is successfully established, the user data contained in the output buffer of the
CP 440 is sent to the communication partner with the selected transmission parameters. The
partner monitors the times between incoming characters. The interval between two
characters must not exceed the character delay time.
If the communication partner sends the NAK control code during an active send operation,
the procedure aborts its transmission of the block and tries again as described above,
beginning with connection setup. If a different code is sent, the procedure first waits for the
character delay time to expire and then sends the NAK code to change the mode of the
communication partner to idle. Then the procedure starts to send the data again with the
connection setup STX.
Releasing a Send Connection
Once the contents of the buffer have been sent, the procedure adds the codes DLE, ETX
and in the case of 3964(R) only the block checksum BCC as the end code, and waits for an
acknowledgment code. If the communication partner sends the DLE code within the
acknowledgment delay time, the data block has been received without errors. If the
communication partner responds with NAK, any other code (except DLE), or a damaged
code, or if the acknowledgment delay time expires without a response, the procedure starts
to send the data again with the connection setup STX.
After the defined number of attempts to send the data block, the procedure stops trying and
sends an NAK to the communication partner. The CP 440 reports the error to the SEND_440
function block (STATUS output parameter).
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Point-to-point connection CP 440 Installation and Parameter Assignment
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Manual, 09/2007, A5E00057742-03
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