Can't access registers above Q127 on Step 7-300 PLC

[sanger]

We're have an S7-300 (313C-2 DP) configured to talk to another PLC via a DP-DP coupler. We configured the I/O for the coupler with 3 blocks of 64-bytes and are using BLKMOV to copy the data to the output QB64 through QB255. Data only gets through to the otherside of the coupler up to QB127.

When we try to monitor the QB registers with a Variable Table we can see everything up to QB127 but everything after that display a status of unavailable. Even tried going to the Hardware Configuration screen, clicking an address block above QB127 and selecting Monitor/Modify but it still displays all addresses as unavailable. Tried monitoring PQB as well but no luck.

Any ideas?

 

[KalleOlsen]

Your PLC apperantly has 128 bytes I/O image area, and PQ's cannot be viewed. Check in the HW-Conf if the process image area can be expanded.

OR

Change BLKMOV with 3 calls with DPWRITE (one call per block (line) in the DP configuration).

Kalle

 

[grnick50]

Or you can try addressing as PIW or PIB etc.
In some CPUs you from the HW configuration you can extend the available bytes of the Process Image.
What is the CPU type?

 

[sanger]

From the documentation I have read you have to use Peripheral I/O addresses (PIB, PQB) to access input and output addresses outside of the CPU's Process Image. Unfortunately the BLKMOV instruction does not work with Peripheral areas so we would be forces to do a few hundred individual move instructions to transfer the data.

I hope there is a better way.

 

[grnick50]

Please see the attached screenshot. Is this not available for your CPU?
Why cant you just use PIWxxx addressing? Why do you need "a few hundred individual move instructions to transfer the data"? I mean if we are talking for DIs and DOs you could move PID and PQD to a memory location and then extract the bits.

Regards

 

[KalleOlsen]

... We configured the I/O for the coupler with 3 blocks of 64-bytes and are using BLKMOV to copy the data to the output QB64 through QB255. ...

How is the consistency set up? Byte/word/total?

If you use 'Total', you must use DPWRITE (once per 64byte-block).

If not, you must use L / T or make a loop that does the transfer (f.x. PQD by PQD).

If you search this forum, you will find more info on the topic.

Kalle

 

[sanger]

The particular process did not allow for increasing the Process Image beyond 128 bytes.

Ended up copying the array DWORD by DWORD to the PQD registers and it is working.