PROFIBUS issue

A few things.

If you force Q166.0 to false, does it immediately get set back to true?

What is the update rate of your PB coupler?

If you sort your entire PLC tag table so all the Q's are shown together, is there a tag mapped to QD164? 

Are there any yellow tags which portal uses to note duplicate or overlapping tags?

Can you show us a screenshot of cross reference for Q166.0 or QB166 or QW166 or QD164 or QD166?  If any of those have "write" in the cross reference, you will need to figure out why and fix it.

ZhZL

Hello!

I am working on a self-proof project. I configured the PROFIBUS COUPLER with I/O module (32bytes) and start running "online". The Q166.0 (in slave 2) sends out alternative signal while I166.0 (in slave_1) should receive the alternated signal. But I166.0 value is "1" all the time. Other signals works correctly. Please see the attachements.

At first, I thought the problem was caused by address overlapping. I changed the I/O module address in the module but the problem remained.

Do someone encounter the same problem before? I am confused...

Hope to hear from you soon.

Best regards,

ZhZL

What I meant was the change the Q166.0 in the PLC with the Q166.0 in it, not the remote PLC.

In the "used by", FC2 is writing to Q166.0.  What is on network 1?  How often is FC2 called?

Is it possible your remote plc is setting Q167.0 as the "low byte", or it is received with opposite "endian" style? 

ZhZL

Hello!

For the first question, the tag keeps 'false' when it is forced from 'true-> false'. Please see picture.

The signal update rate through PB is 500 ms, Pb bus speed is set to 5Mbps.  

There is no yellow tags in the program. 

I provide the Q items (before 166 and after 166) for your check.For your information, from Q166 to Q 197 is a 32 bytes structure.  

Look forward hearing from you!

Best regards,

ZhZL

If your remote PLC is using let's say big endian (google for what that means), and the local PLC is using little endian, the byte order may be swapped in the words sent between the devices.

Easy way to know is to toggle Q167.0, and Q166.0 opposite each other in the Q side, and in the I166/167, see where the bits toggle.

You can view QW166 and see all 16 bits to see if the 2nd byte's 0-bit is toggling.

If that is the case, you will want to byte swap (using the swap instruction) your 16 words (32 bytes) before using them.

ZhZL

Hello.

okay.I misunderstood you. The I 166.0 in remote PLC doesn't react at all with forcing value to 'false' in the Q166.0 PLC. The value is always 'true'

FC2 is the block 'moving ' the 32 bytes structure to Q166-Q197, the call rate is 500ms. Q 166.0 is the one needs to alternate at frequency of 1Hz.  Q168.0, 174.0, 178.0, 182.0 can be sent and read fine (these signal doesn't alternate often). 

What does it "Is it possible your remote plc is setting Q167.0 as the "low byte", or it is received with opposite "endian" style?" Could you explain a little bit?

Best regards,

ZhZL

Hello ZhZl

I'll hazard a guess and say you have the "DIA" dip switch set to ON position on the DP/DP coupler. 

If so, the first bit in the first configured input byte indicates that the data is valid (bit is "1") or invalid (bit is "0") and can thus not be used for your normal data exchange.

See also chapter 4.2.2 of the DP/DP coupler manual for more.