Siemens SIMATIC S7-400H System Manual page 56

Assembly of a CPU 41x–H
5.3 Status and error displays
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
Lit Irrelevant
Irrelevant Lit
Irrelevant Dark
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
INTF EXTF
Lit Irrelevant
Irrelevant Lit
Irrelevant Irrelevant
56
Meaning
RACK1
Irrelevant CPU controls switched I/O
Dark CPU on rack number 0
Lit CPU on rack number 1
Meaning
FRCE
Irrelevant An internal error was detected (programming or parameter
assignment error).
Irrelevant An external error was detected (i.e. an error whose cause is not in the
CPU module).
Lit A force request is active.
System Manual, 03/2012, A5E00267695-11
S7-400H