Receiving Data With 3964(R); Figure 2-6 Data Traffic When Receiving With The 3964(R) Procedure - Siemens Simatic S7-300 CP 341 User Manual

Basic Principles of Serial Data Transmission
2.4 Data Transmission with the 3964(R) Procedure
2.4.5

Receiving Data with 3964(R)

Receiving data with 3964(R)
The figure below illustrates the transmission sequence when data is received with the
3964(R) procedure.
Figure 2-6
Note
As soon as it is ready, the 3964(R) procedure sends a single NAK character to the
communication partner to set the latter to idle.
Connection setup for receiving
In the idle state, when there is no send request to be processed, the procedure waits for the
communication partner to set up the connection.
If no empty receive buffer is available during a connection setup with STX, a wait time of
400 ms is started. If there is still no empty receive buffer after this time has expired, the
CP 341 reports the error (error message at STATUS output of the FB). The procedure sends
a NAK character and returns to the idle state. Otherwise, the procedure sends the DLE
character and receives the data.
If the procedure receives any control character (except for STX or NAK) while in idle state, it
waits for the character delay time to expire and then sends the NAK character. The CP 341
reports the error to the P_RCV_RK function block (STATUS output parameter).
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Data traffic when receiving with the 3964(R) procedure
CP 341 Point-to-Point Communication, Installation and Parameter Assignment
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Manual, 09/2008, A5E02191071-01