Siemens Simatic S7-400 - Handling Corrupt Data

2.5.5 Handling Corrupt Data
Reaction to Corrupt Data
The 󹪝gure below illustrates how corrupt data is handled with the 3964(R) procedure.
CP 440
STX
DLE
DLE
ETX
BCC
NAK
¡
¡
¡
¡
¡
¡
T
Communication
partner
1st byte
1st data byte
nth byte
nth data byte
Start code (02H)
Pos. acknowledgment (10H)
End code (10H)
End code (03H)
3964(R) only
Neg. acknowledgment (15H)
Connection
setup
User data
Connection
cleardown
Receiving data
New setup attempt
Figure 2-19 Data tra󹪟c when receiving corrupt data
When DLE, ETX, BCC is received, the CP 440 compares the BCC of the communication partner
with its own internally calculated value. If the BCC is correct and no other receive errors occur,
the CP 440 responds with DLE.
Otherwise, the CP 440 responds with an NAK and waits the block wait time (T) of 4 seconds for
a new attempt. If after the de󹪝ned number of transmission attempts the block cannot be
received, or if no further attempt is made within the block wait time, the CP 440 aborts the
receive operation.
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
46 Equipment Manual, 03/2022, A5E00057742-AE