Siemens SIMATIC S5-100U System Manual page 424

Function Modules
Function
The diagnostic module is used for monitoring the S5-100U I/O bus. LEDs on the front panel display
the signal states of the control lines and the supply voltage for the I/O bus.
• IDENT
The programmable controller executes an IDENT run after each change from STOP to RUN. It
executes an IDENT run after any changes in the configuration in order to determine the current
configuration. The IDENT LED lights up briefly. If the LED lights up in the RUN mode, this
indicates that a faulty I/O module has been plugged in.
• CLEAR
The CLEAR signal line is "1" only in the STOP mode in normal operation.
The outputs of the output modules are disabled.
If CLEAR is "1" in the RUN mode, the control line itself may be defective (no contact).
• LATCH/CLOCK
These two control lines control data interchange between the CPU, the I/O bus, and the I/O
modules.
During normal operation, both LEDs must flash (programmable controller in RUN mode).
The flashing frequency provides information on the speed of the serial bus.
If both LEDs show a steady light in the RUN mode, the bus unit that the diagnostic module is
plugged into is defective.
• DATA/DATA-N
The alternate lighting up of the DATA and DATA-N LEDs indicates data flow on the I/O bus.
If these two LEDs show a steady light (as in the case of the LATCH and CLOCK LEDs), this
indicates that the bus unit that the diagnostic module is plugged into is defective.
• U1 8 V
If the supply voltage of a slot remains at a value U1 8 V, proper functioning of the I/O
modules is no longer guaranteed. The low supply voltage can be explained by an excessively
high bus load (> 1 A).
If this LED flickers, noise pulses are superimposed on the supply voltage U1 (e.g., by the
coupling of noise pulses).
The LED lights up briefly if the programmable controller is switched on or off.
• U1 > 8 V
The supply voltage of the I/O bus is functioning correctly.
15-10
S5-100U
EWA 4NEB 812 6120-02b