Assembly of a CPU 41x–H
5.3 Status and error displays
S7-400H
56 System Manual, 03/2012, A5E00267695-11
MSTR, RACK0, and RACK1 LEDs
The three LEDs MSTR, RACK0, and RACK1 provide information about the rack number set
on the CPU and show which CPU controls the switched I/O.
LED
MSTR RACK0 RACK1
Meaning
Lit Irrelevant Irrelevant CPU controls switched I/O
Irrelevant Lit Dark CPU on rack number 0
Irrelevant Dark Lit CPU on rack number 1
INTF, EXTF, and FRCE LEDs
The three LEDs INTF, EXTF, and FRCE provide information about errors and special events
in the user program execution.
LED Meaning
INTF EXTF FRCE
Lit Irrelevant Irrelevant An internal error was detected (programming or parameter
assignment error).
Irrelevant Lit Irrelevant An external error was detected (i.e. an error whose cause is not in the
CPU module).
Irrelevant Irrelevant Lit A force request is active.
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