Siemens SIMATIC S5 CP 523 Manual page 241

Summary
Table A-14. Status Byte in Communications Mode (CP to CPU) ( 7.4)
Byte 0
Bits 4 to 7 Bits 0 to 3
0 0
X 1
X 3
X 7
X 8
0 F
1 X
2 X
3 X
4 X
8 X
Coordination information (only after "Coordinate data transfer" request)
5 9
*
5 A
*
5 B
*
5 C
*
5 D
5 E
*
X= signal state not significant for other half-byte
* These errors are not flagged until a "coordinate data transfer" request to receive data has been serviced for this
message frame.
A-12
No error
No memory submodule
Entries in job buffer (for parameter setting requests only)
No battery backup
Job buffer full (for parameter setting requests only)
CP restart in progress
Clock defective
Default time of day set
Time of day/date error
Illegal job request
Hardware fault
Character delay time exceeded
Parity error
Receive after XOFF or receive after DTR = 0
Message frame exceeds 256 bytes
Permanent break in peripheral device cable
Receive mailbox overflow
Status
EWA 4NEB 811 6044-02a
CP 523