Siemens SIMATIC S5-90U System Manual page 479

S5-90U/S5-95U
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"
mode and after any changes in the configuration in order to determine the current configuration
of the programmable controller. 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 only "1" 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 8V
If the supply voltage of a slot remains at a value U1 8V, 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 > 8V
The supply voltage of the I/O bus is O.K.
EWA 4NEB 812 6115-02b
Function Modules
16-11