[etherlab-users] domain process data persistence

[Thomas Bitsky, Jr.]

I think you're thinking of it wrong. The data isn't cleared, it's replaced
by the actual value on the field bus. So, if you don't write the value out
to update the field bus, then the packet gets returned with the value that
is out there.

Thomas C Bitsky Jr
Lead Developer and Application Engineer
ADC | automateddesign.com
(Sent from my mobile device.)
On Oct 6, 2012 4:14 AM, "Thomas Paoloni" <thomas at digithom.it> wrote:

> Hi all,
>
> even if I'm dealing with ethercat since more than one year, I'm in front
> of a very basic question ...
> As from I can see, the data in master->slave direction in the domain_pd
> area are not preserved from an update to another.
> I'mean that I need to write out data to domain_pd area at each cycle, even
> if I data is not changed and theoretically I don't need to update some
> parts of the pdo area.
>
> Just applying this to the basic example in examples/user
>
> void cyclic_task()
> {
>     int i;
>
>     // receive process data
>     ecrt_master_receive(master);
>     ecrt_domain_process(domain1);
>
>     // check process data state (optional)
>     check_domain1_state();
>
>     if (counter) {
>         counter--;
>     } else { // do this at 1 Hz
>         counter = FREQUENCY;
>
>         // calculate new process data
>         blink = !blink;
>     }
>
>     EC_WRITE_U8(domain1_pd + off_dig_out, blink ? 0x06 : 0x09);
>
>     // send process data
>     ecrt_domain_queue(domain1);
>     ecrt_master_send(master);
> }
>
>
> moving the EC_WRITE_U8 inside the if condition (after the blink=!blink)
> will not work, because the blink bit is cleared from the pdo area after the
> process data has been sent.
>
> This means that I should keep a copy of the process data and write it on
> the domain1_pd each time.
> Is this right or I'm missing something ?
>
>
> Thanks,
> Thomas.
>
>
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