Thanks all for the concern.

The I and Q addresses do exist at the PLC, because the 8-point DI modules were installed at slot 0 and 1, and the 8-point DO modules were installed at slot 2 and 3. There isn't onboard I/O bits for the PLC.

Referring to STEP 5 V6.6 Manual page 300 (3-247), the HELP key to be depressed to find out more information for ISTACK. However, there isn't any key asigned for HELP on ISTACK display.I tried Shift-F8 which normally used for HELP, but it doesn't work. Which key could be used?

Trank

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However, there isn't any key asigned for HELP on ISTACK display....

I found that the ISTACK showed that "Command cannot be interpreted in this PLC." I further found that the version of the CPU is S5-100U CPU100. The instructions in the function block do not supported by the CPU. This caused the CPU went stop immediately once the function block was called. Thanks for the "Insert" key and "IBN-Service".

Trank

I found that the ISTACK showed that "Command cannot be interpreted in this PLC." I further found that the version of the CPU is S5-100U CPU100. The instructions in the function block do not supported by the CPU. This caused the CPU went stop immediately once the function block was called. Thanks for the "Insert" key and "IBN-Service".

Please check "S5-100U Programmable Controller System Manual" Page A-8.