Note that the MAINT LED on the analog on-board I/O is only intended for troubleshooting by
. In normal condition, the MAINT-LED should not light up. However, if the LED is lit
up, please contact "mySupport" at The figure below shows an example of the LED displays (status and error displays) of the
first module of the digital on-board I/O. Remedial measures for diagnostics alarms can be
found in section Interrupts and diagnostics of the digital on-board I/O (Page 138)For the status display, the digital inputs only take into account the filter time of the
corresponding DI and not the filter time of the A/B/N signals of the fast counters (HSC).
For example, a static signal may be displayed when the DI has a configured input delay of
3.2 ms, even though a 100 kHz counter on these inputs still detects edge transitionsThe compact CPU can generate a hardware interrupt for the following events:
● Below low limit 1
● Above high limit 1
● Below low limit 2
● Above high limit 2
You can find detailed information on the event in the hardware interrupt organization block
with the "RALARM" (read additional interrupt information) instruction and in the STEP 7 (TIA
Portal) online help.
The start information of the organization block includes information on which channel of the
analog on-board I/O triggered the hardware interrupt. The figure below shows the
assignment to the bits of double word 8 in local dataIf the two high limits 1 and 2 are reached at the same time, the analog on-board I/O always
signals the hardware interrupt for high limit 1 first. The configured value for high limit 2 is
irrelevant. After processing the hardware interrupt for high limit 1, the compact CPU triggers
the hardware interrupt for high limit 2.
The analog on-board I/O behaves accordingly when the low limits are reached
simultaneously. If the two low limits 1 and 2 are reached at the same time, the analog onboard
I/O always signals the hardware interrupt for low limit 1 first. After processing the
hardware interrupt for low limit 1, the analog on-board I/O triggers the hardware interrupt for
low limit 2.A diagnostics alarm is output for each diagnostics event and the ERROR LED flashes on the
analog on-board I/O. The diagnostics alarms can, for example, be read out in the diagnostics
buffer of the CPU. You can evaluate the error codes with the user program.Resistance of encoder circuit too
high
Use a different encoder type or modify the
wiring, for example, using cables with
larger cross-section
Interruption of the cable between the
analog on-board I/O and sensor
Connect the cable
Channel not connected (open) • Disable diagnostics
• Connect the channel
Overflow 7H Measuring range exceeded Check the measuring range