Receiving Data With 3964(R) - Siemens SIMATIC S7-400 Equipment Manual

D: Default state
W: Waiting for character reception
2.5.4

Receiving Data with 3964(R)

Process of Data Transmission when Receiving
The figure below illustrates the transmission sequence when data is received with the 3964(R)
procedure.
Communication
partner
Connection
Connection
cleardown
Figure 2-16
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.
Establishing a Receive Connection
In idle mode, when there is no send request to be processed, the procedure waits for the
communication partner to establish 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 elapsed, the CP 440 reports
the error (error message at the STATUS output of the FB). and the procedure sends a NAK and
returns to idle mode. Otherwise, the procedure sends a DLE and receives the data.
If the idle procedure receives any control code except for STX or NAK, it waits for the character
delay time to expire, then sends the code NAK. The CP 440 reports the error to the RECV_440
function block (STATUS output parameter).
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE
setup
User
data
Data Traffic when Receiving with the 3964(R) Procedure
Basic Principles of Serial Data Transmission
2.5 Data Transmission with the 3964(R) Procedure
STX
DLE Pos. acknowledgment (10H)
1st byte
2nd byte
¡
¡
nth byte
DLE
ETX
BCC
DLE Pos. acknowledgment (10H)
CP 440
Start code (02H)
1st data byte
2nd data byte
¡
¡
nth data byte
End code (10H)
End code (03H)
3964(R) only
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