Siemens SIMATIC S7-400 Reference Manual page 24

Structure of a CPU 41x
Error Displays and Points to Note, All CPUs
The three LEDs INTF, EXTF and FRCE on the front panel of a CPU inform you
about the errors and points to note during the execution of the user program.
LED
INTF EXTF
H x
x H
x x
H = LED lights up; x = LED status is irrelevant
The LEDs BUSF1 and BUSF2 indicate errors in connection with the MPI/DP
interface and the PROFIBUS DP interface.
LED
BUS1F BUS2F
H
x
B
x
H = LED lights up; B = LED flashes; x = LED status is irrelevant
1-12
FRCE
x An internal has been detected (program or configuration error) or
the CPU is performing a CiR.
x An external error has been detected (in other words, the cause of
the error cannot be traced back to the CPU module).
H A force request is active.
x An error has been detected at the MPI/DP interface.
H An error has been detected at the PROFIBUS DP interface.
x DP master: One or more slaves at PROFIBUS DP interface 1
are not replying.
DP slave: not addressed by the DP master
B DP master: One or more slaves at PROFIBUS DP interface 2
are not replying.
DP slave: not addressed by the DP master
Meaning
Meaning
Automation System S7-400 CPU Specifications
A5E00165965-01