Trouble reading flexIO analog from a S7 drop

(I've sent the following message to www.control.com prior to this sending.)


The system is as follows:
S7/400 has 6 profibus drops, all are Rockwell FLEX IO interfaced via "Prosoft 3170-PDP" interface.

I've added the seventh drop - addressed as #10, and setup with following modules in this physical order.:
1794 IB16 - 16 way input , "in bytes" 502-3
1794 IB16 - 16 way input , " 504-5
1794 OB16 - 16 way output, "out bytes" 506-7
1793-IE4 - 4 way analog in, "in bytes" 515-532, "out bytes" 515-516
1794 OB16 - 16 way output, "out bytes" 510-511
1794 OB16 - 16 way output, "out bytes" 508-9

I can see the digital inputs, & force digital outputs. But can not see data in bytes "in" or "out" relating to the analogue module.

Further this occurs with my software "FB", dormant, ie not called by OB1.

If it's called the PLC STOPS on OB85 (which was not loaded into PLC). (OB82, 86 & 122 are loaded into the S7, thus failure does not happen on these). Diagnostic trip error for OB85 reads "I/O access error when transferring the process image table to the output modules".

I figure that I can load OB85 into S7 which should prevent the "Stop". But, what will happen to the IO image table. Does it stay unchanged or do all inputs go to "0", when PLC can't read the drop for example. May be undesirable if the image table is frozen.

Secondly why is Analog not visible to the PLC?
Is it its placement between digital modules.
Or the allocated byte numbers.

Comments on any of the above is appreciated, since I'm on a bit of a steep S7 learning curve.

For purose of completeness & info:

I have resolved the problem today thanks to Siemens Support centre here in Sydney.

(This is my re-telling of the explanation to me, - may not be exactly correct, but close enough.)

It turns out that the addressing byte value is incorrect. It must be an even number. Also only digital IO (and analog IO) can be allocated to bytes up to 512. Analogs can be configured above 512. But these need to be referenced in software as "PIW", instead of "IW".

I did have enough memory below, so I allocated 18 bytes starting with byte 480.

Further I downloaded OB85 into the PC, beside 82, 86 & 122 (already downloaded). Then I killed the power to the remote drop. This caused error lamps on the PLC diagnostics - BUT PLC kept running. Further the IO memory map was reset to "0" values - exactly what I wanted - which means that the code should naturally shut the process, simply as the result of "reset" input states.