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Basic Principles of Serial Data Transmission

2.4 Data Transmission with the 3964(R) Procedure

PtP coupling and configuration of CP 340

Manual, 04/2011, A5E00369892-03

Releasing a Receive Connection

If transmission errors occur during receiving (lost character, frame error, parity error, etc.),

the procedure continues to receive until the connection is shut down, then an NAK is sent to

the communication partner. A repetition is then expected. If the undamaged block still cannot

be received after the number of repeat attempts defined on parameter assignment, or if the

communication partner does not start the repetition within a block wait time of 4 seconds, the

procedure aborts the receive operation. The system program then reports the error to the

function block P_RCV (output parameter STATUS).

When the 3964 procedure detects a DLE ETX character string, it stops receiving and

confirms that the block has been successfully received by sending a DLE character to the

communication partner. When errors are found in the received data, it outputs a NAK signal

to the communication partner. A repetition is then expected.

If the 3964R procedure detects the string DLE ETX BCC, it stops receiving. If the BCC is

correct and no other receive errors have occurred, the CP 340 sends the code DLE to the

communication partner. If the BCC is correct and no other receive errors have occurred, the

3964R procedure sends a DLE and returns to idle mode. If the BCC is faulty or a different

receiving error occurs, an NAK is sent to the communication partner. A repetition is then

expected.

Note

As soon as it is ready, the 3964(R) procedure sends a single NAK to the communication

partner to set the latter to idle.

Siemens SIMATIC CP 340 User Manual

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