Siemens SIMATIC S5-90U System Manual page 105

S5-90U/S5-95U
5 Diagnostics and Trouble Shooting
5.1 Diagnostic Byte
The diagnostic byte offers you another means of controlling the process sequence.
The diagnostic byte displays the following:
• Whether a counter has reached the comparison value (counter overflow)
• Whether and where an interrupt was triggered
• Whether the power supply for the onboard I/Os has failed (only for the S5-95U)
• Whether a battery backup is available (only for the S5-95U)
The diagnostic byte for both programmable controllers is in input byte (IB) 35.
Diagnostic Byte Assignment for the S5-90U
Interrupt at I 33.0
No interrupt at I 33.0
Counter overflow
No counter overflow
X=insignificant
Signal status "1" in one of the diagnostic bits signifies that:
• Since the last start-up, an interrupt has occurred. This does not mean that interrupt processing
is taking place.
Signal status"0" in one of the diagnostic bits signifies one of the following conditions.
• Since the last start-up, no interrupt has occurred.
• The user erased the respective diagnostic bit after the interrupt. It does not signify that the
corresponding interrupt processing is complete.
EWA 4NEB 812 6115-02b
Bit no.: 7
IB 35 X
1
0
1
0
Figure 5-1. Diagnostic Byte for the S5-90U
Diagnostics and Trouble Shooting
6 5 4 3 2
i
X X X X
1 0
C
X
5-1