Siemens SIMATIC S5-100U System Manual page 440

Function Modules
• Diagnostic Byte (Byte 1)
The diagnostic byte is byte 1 of the first input word. Byte 0 has no significance.
The diagnostic byte provides information on the following items:
- Preset position resolution
- Preset mode
- Status of setpoints
- Signal status of the sync bit for position decoding
Position resolution
not possible
Mode
Position decoding
Counter overflow
No counter overflow
Setpoint 2 reached
Setpoint 2 not reached
Setpoint 1 reached
Setpoint 1 not reached
Sync bit set
Sync bit not set *
X = irrelevant
*
If the sync bit is not set, a reference point approach must be implemented before operation
can continue in the Position Decoding mode.
15-26
Bit No.: 7 6 5
X R R
0 1
single
1 0
double
1 1
quadruple
0 0
1
Counter 0
1
0
1
0
1
0
1
0
Figure 15-15. Diagnostic Byte
4 3 2 1 0
P/C OV S S Sy
2 1
S5-100U
EWA 4NEB 812 6120-02b