Siemens Simatic S7-200 System Manual page 178

Network Communications and the S7-200 CPU
DP LED Status Indicator
The CPU 215 has a status LED on the front panel to indicate the operational state of the DP
port:
After the CPU is turned on, the DP LED remains off as long as DP communication is not
attempted.
Once DP communication has been successfully initiated (the CPU 215 has entered data
exchange mode with the master), the DP LED turns green and remains on until data
exchange mode is exited.
If communication is lost, which forces the CPU 215 to exit data exchange mode, the
DP LED turns red. This condition persists until the CPU 215 is powered off or data
exchange is resumed.
If there is an error in the I/O configuration or parameter information that the DP master is
writing to the CPU 215, the DP LED flashes red.
Table 9-12 summarizes the status indications signified by the DP LED.
Table 9-12 DP LED Status Indicator
LED State
Off
Flashing red
Green
Red
9-22
Status Indication Description
No DP standard communication attempted since last power on
Error in parameter assignment or configuration, CPU not in data exchange mode
Currently in data exchange mode
Dropped out of data exchange mode
S7-200 Programmable Controller System Manual
C79000-G7076-C230-02