Siemens SIMATIC S5-95U - Page 55

S5-95U, Second Serial Interface Computer Link with 3964(R) Transmission Protocol
Example of incorrect data transmission:
Figure 3-13 Incorrect Data Transmission
NAK
DLE
DLE
DLE
nth char.
1st char.
STX
Communication partner
High priority
S5-95U 3964(R) driver
Low priority
* BCC only with 3964R transmission protocol
BCC *
ETX
DLE
STX
NAK
STX
a a
a a
a a
a a
a a
a a
a a
a a
a a
a a
.
.
DLE
nth char.
1st char.
a a a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a a a
.
.
ETX
BCC *
Incorrect
buildup attempt
Incorrect
send attempt:
BCC invalid
EWA 4NEB 812 6095-02 3-23