Siemens SIMATIC S5 Manual page 92

Data Transmission Using a Standard Connection
Structure of the Receive Coordination Byte (CBR)
Figure 4-7 shows the structure of the receive coordination byte (CBR).
Bit 7 6 5
W/R R
R: Read only
W/R: Write / read
Reserved bit
Warning
!
If you write in bit 6 of CBS, the bus might enter an undefined state.
Bit 6 is not available to the user.
Figure 4-7. Structure of the Receive Coordination Byte (CBR) for a Standard Connection
4-8
CBR
4 3 2 1
R
0
R
0: No error
1: Error during the last data transmission
(Bits 2 and 5 describe the error cause in more
detail.)
0: No error
1: Receive mailbox error (The DB is not
available.) Received data stay stored. A new
receive request can transfer the received data
to the receive mailbox once the error has been
corrected.
0: The L2 interface is not overloaded.
1: The L2 interface is overloaded.
0: The user program can access the receive
mailbox. (The operating system has no access
to the receive mailbox.)
1: The operating system can accept data in the
receive mailbox. (The user program has no
access to the receive mailbox.)
S5-95U, SINEC L2
EWA 4NEB 812 6112-02