Siemens SIMATIC CP 340 User Manual page 40

Basic Principles of Serial Data Transmission
2.4 Data Transmission with the 3964(R) Procedure
Receiving with the 3964(R) procedure
The figure below illustrates receiving with the 3964(R) procedure.
Receiving with procedure 3964(R) (part 1)
Character not equal to STX or faulty
character
NAK or BREAK
Waiting for character
time delay
Send NAK
Figure 2-9 Flow diagram of receiving with the 3964(R) procedure (part 1)
R: Counter for retries
D: Default state
40
Send request
G
S T X
W + 1
W = 0
Add waiting time to free
receiving buffer
No
Is receiving buffer
free ?
Yes
Has waiting time of 400
Send DLE Send NAK
2
1
STX received after
3
expected repeat
Initialization conflict, own
4 priority low
Waiting 50 ms
No
ms expired ?
G
PtP coupling and configuration of CP 340
Manual, 04/2011, A5E00369892-03