Siemens SIMATIC S7-1500 Manual page 76

Channel LEDs
The CHn.A, CHn.B, CHn.N and DIn.m LEDs indicate the current level of the associated
signals. The LEDs of the DQn.m digital outputs indicate the desired state.
The flashing frequency of the channel LEDs is limited to approximately 12 Hz. If higher
frequencies are present, the channel LEDs will flash at 12 Hz instead of indicating the
current status.
When an SSI absolute encoder is used, the CHn.D and CHn.C LEDs are lit green during
transfer of the encoder frame and are lit red if an error occurred. The CHn.D and CHn.C
LEDs are off when no encoder frame is being transferred or if an error has occurred for
which the diagnostic interrupt is not enabled.
Table 5- 3
CHn.m/DIn.m/DQn.
(CHn.m/DQn.m)
Technology module TM PosInput 2 (6ES7551-1AB00-0AB0)
Manual, 06/2018, A5E03982218-AB
Status displays CHn.m/DIn.m/DQn.m
LEDs
m
Counter input/digital input/digital output
at 0 level
Off
Counter input/digital input/digital output
at 1 level
On
Diagnostic alarm: e.g. wire break,
short-circuit
On
Meaning
Interrupts/diagnostic messages
5.1 Status and error display
Remedy
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Check the wiring or the connected
load.
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