It appears that the situation is being analyzed by the display of data through an HMI.

If it were me, I'd disconnect the HMI and use Modscan or ModPoll to poll one drive "write, then read" and see what the traffic looks like after the read request to see if the HMI is delaying the update somehow or to see if noise is actually disrupting the traffic.  Modscan will throw errors if the packets are bad and the packet counter shows the number of Good transactions.

humperdoo

Just an idea, do you use cascaded read and write requests ? Modbus rtu works as serial communication and starting another read or write before the previous one is finished can cause stuff like that.

 I am using a counter up move between read and write requests.

This counter is increased when using a 0.1 Hz pulser and if all busy output off all read and write modules is false. ( see the attachment)

msgsadek

I am using a counter up move between read and write requests.

This counter is increased when using a 0.1 Hz pulser and if all busy output off all read and write modules is false. ( see the attachment)

I see trouble. Consider sharing more of your program as you are currently doing.

RE: if all busy output off

This is not what the code is doing. It is increasing the count if at least one of the outputs is off.

qwazee

 

msgsadek

I am using a counter up move between read and write requests.

This counter is increased when using a 0.1 Hz pulser and if all busy output off all read and write modules is false. ( see the attachment)

I see trouble. Consider sharing more of your program as you are currently doing.

RE: if all busy output off

This is not what the code is doing. It is increasing the count if at least one of the outputs is off.

 OH yes,

You are right, so I must put them in series and not in parallel.

I will try that and give feedback

msgsadek

OH yes,

You are right, so I must put them in series and not in parallel.

I will try that and give feedback

To begin with, the idea of using a time pulse is a sure way for looking for trouble. It is better to have the DONE or ERROR state of a communication block trigger the next communication block.

You can probably do this with the master counter idea you are using (I won't). The idea within the frame of what you have done is that any DONE or ERROR will trigger the master counter to increase. 

Consider to have a counter increase each time an ERROR is detected. This will help you identify if there are problems in the communications. Also time how long it takes for your master counter to go from start to finish.

You code in LAD. Siemens has switched over to SCL in their examples. So it is difficult to suggest an example application for you. It might be better to try and smooth out the problems you have within the framework you have already created. For this purpose consider placing a piece of your program in the forum for people to evaluate and comment.

Good luck.

To changed comment:
There is an error on one of the slaves.
BUSY will keep high until the trigger is removed (if I remember).
See earlier comments for alternate solution.

qwazee

 

msgsadek

OH yes,

You are right, so I must put them in series and not in parallel.

I will try that and give feedback

To begin with, the idea of using a time pulse is a sure way for looking for trouble. It is better to have the DONE or ERROR state of a communication block trigger the next communication block.

You can probably do this with the master counter idea you are using (I won't). The idea within the frame of what you have done is that any DONE or ERROR will trigger the master counter to increase. 

Consider to have a counter increase each time an ERROR is detected. This will help you identify if there are problems in the communications. Also time how long it takes for your master counter to go from start to finish.

You code in LAD. Siemens has switched over to SCL in their examples. So it is difficult to suggest an example application for you. It might be better to try and smooth out the problems you have within the framework you have already created. For this purpose consider placing a piece of your program in the forum for people to evaluate and comment.

Good luck.

To changed comment:
There is an error on one of the slaves.
BUSY will keep high until the trigger is removed (if I remember).
See earlier comments for alternate solution.

 Dear qwazee,

I program in SCL and I have good idea on SCL.

If you have any example that I can use in this application even if it is in SCL I would appreciate that alot.

On the other hand, I will take your notes into consideration and try to apply them to figure out what is wrong.

msgsadek

 Dear qwazee,

I program in SCL and I have good idea on SCL.

If you have any example that I can use in this application even if it is in SCL I would appreciate that alot.

On the other hand, I will take your notes into consideration and try to apply them to figure out what is wrong.

Consider the use of this wrapper..
(as provided by Mr. Ola Bjørnli)
https://github.com/rexhip/rexhip

I am happy with it.. Even if the drive I was controlling was not on the list, I found it easy to use the building blocks it provided. The messiness of sequencing is also handled.

Else..
How do you establish a MODBUS-RTU communication with STEP 7 (TIA Portal) for the SIMATIC S7-1200?

Applications & FAQ: "modbus sequencer"