Siemens SIMATIC CP 440 Manual page 53

Receiving with the 3964(R) Procedure (Part 2)
The figure below illustrates receiving with the 3964(R) procedure.
Initialization conflict
noted, low priority
Times: T
char. delay time
W = transmission attempt counter
BCC only with 3964(R)
Immediate return to initial state at line break (BREAK)
Figure 2-20
Point-to-point connection CP 440 Installation and Parameter Assignment
A5E00057742-02
4
Start T
char. delay time
Correct
character
except
Wait to
for DLE
receive
characters
DLE
Start T
char. delay time
Dual DLE
Wait for
Note NAK
ETX
Characters
ETX
except ETX, DLE
3964
Start T
NAK noted
Send DLE
Receipt completed
3 G
= 220 ms, T = 4 s
Block
Flow Diagram of Receiving with the 3964(R) Procedure (Part 2)
Basic Principles of Serial Data Transmission
Note
NAK
Invalid character
T > T
char. delay time
T > T
char. delay time
3964(R)
char. delay time
T > T
char.
Wait for
delay time
BCC incorrect
BCC
BCC
Send NAK
W > 5
Note repetition
expected, start T
Wait for
STX
1
W <= 5
BLOCK
T >
T
BLOCK
G
STX
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