Siemens SIMATIC CP 440 Manual page 51

Sending with the 3964(R) Procedure
The figure below illustrates sending with the 3964(R) procedure.
G
High
priority
Low
priority
BCC only with 3964(R)
x = setup attempt counter
T =500 ms (3964(R) T
ADT
W = transmission attempt counter
Immediate return to initial state at line break (BREAK)
Figure 2-18
Point-to-point connection CP 440 Installation and Parameter Assignment
A5E00057742-02
2
W = 1
3
x = 1
Send STX
Start T
Wait for DLE
STX
acknowledg-
ment
Send block,
poss.
duplicate DLE
Send DLE,
ETX
1
3964
Start T
Wait for DLE
acknowledg-
ment
G
=2s)
ADT
Flow Diagram of Sending with the 3964(R) Procedure
Basic Principles of Serial Data Transmission
Intention to
send
G
Send NAK
x > 6
x <= 6
x + 1
ADT
T > T ,
ADT
character except
DLE, STX or
invalid characters
DLE
Receipt not
permitted
Send NAK
3964(R)
Send BCC
ADT
T > T ,
ADT
character except
DLE or invalid
character
DLE
Sending completed
G
Send NAK
x > 6
x <= 6
W + 1
2-33