Siemens Simatic S7-400

D: Default state
W: Waiting for character reception
2.5.4 Receiving Data with 3964(R)
Process of Data Transmission when Receiving
The 󹪝gure below illustrates the transmission sequence when data is received with the 3964(R)
procedure.
CP 440
STX
DLE
DLE
ETX
BCC
DLE
¡
¡
¡
¡
Communication
partner
1st byte
2nd byte
1st data byte
2nd data byte
nth byte nth data byte
Start code (02H)
Pos. acknowledgment (10H)
End code (10H)
End code (03H)
3964(R) only
Pos. acknowledgment (10H)
Connection
setup
User
data
Connection
cleardown
Figure 2-16 Data Tra󹪟c when Receiving with the 3964(R) Procedure
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 bu󹪜er is available during a connection setup with STX, a wait time of 400 ms
is started. If there is still no empty receive bu󹪜er 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).
Basic Principles of Serial Data Transmission
2.5 Data Transmission with the 3964(R) Procedure
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE 41