Siemens SIMATIC S5 CP 523 Manual page 111

CP 523
If transmission errors occur during reception (characters are lost, framing error, parity error), the
CP continues receiving until the connection is cleared down, transmits NAK to the link partner,
and waits for a retry as described above.
Example of error-free data interchange:
CP 523
3964(R) mode
*) BCC in3964R mode only
EWA 4NEB 811 6044-02a
DLE
DLE
Figure 7-3. Error-Free Data Interchange (Receive)
Communications Mode
Partner in the link
STX
1st character
.
.
.
nth character
DLE
ETX
BCC
*
7-5