did you solve this problem?

I'm facing the same problem.

Modbus master block hangs when i unplug the cable and does not reset.

Even if i set REQ to 0 ad back to one.

The problem is solved by restarting the PLC

Duris_I

Hello,

what PLC HW, CM type, TIA full version?

 Tia V15
Cm is 6es7 541-1ab00-0ab0
Modbus comm load Instruction V3.0
modbus master Instruction V2.4

Yes tia full version

Duris_I

Hello,

check correct sequence of execution of MASTER block, be carefuly if you use clock for REQ, it can hang in some situations. Check in instance DB of MB_MASTER tag MB_STATE value. In case of problem, set it to 0 and start requests again. Better for first correct problems in your code.

 Thanks for the help.

But i can reset the "state" tag and reset REQ but it does not restart the modbus master command.

the routine is called cyclic on a 100ms basis

i attached my code. i can't seem to find the proble/ solution

(the pdf printer of siemens seems to stirr up the order of my networks. )

I found the problem.

When a request is being processed and the connection drops.
if you then change the input parameters the block will hang itself and you will not be able to restore it.

You will have to restart the CPU.

Sou be sure not to change the input parameters while a request is active

Duris_I

Hello,

no, this isn't right solution in my opinion. As I sugested before, clock poll with not correct evulation of output parameters is road to hell. Change of parameters during execution of block is basic problem, then only correct reset sequence (mentioned before with MB_STATE) is only one way, in other case you can init PLC manually if you don't have reset of STATE tag.

 My post was not about the solution, it was about the problem.

You are right about the solution, but you misunderstood my post.

Kamerling

 

Duris_I

Hello,

no, this isn't right solution in my opinion. As I sugested before, clock poll with not correct evulation of output parameters is road to hell. Change of parameters during execution of block is basic problem, then only correct reset sequence (mentioned before with MB_STATE) is only one way, in other case you can init PLC manually if you don't have reset of STATE tag.

 My post was not about the solution, it was about the problem.

You are right about the solution, but you misunderstood my post.

 I know this is an old post.

But I have the same issue, stuck for some time now, unable to find the solution.

First Modbus was working fine for months, second is not workoing at all.

Now I have disabled the first one, only testing the second one, but my block is stuck in "busy" .