[etherlab-dev] Slave to Slave communication

[Dave Page]

On 2015-05-11 22:00, etherlab-dev-request at etherlab.org wrote:
> Have anyone ever run a Safety-over-Ethercat solution via the etherlab-master?

     I have successfully used the EL6900 FSoE PLC, EL1904, and EL2904 
via the IgH master. It is necessary to use TwinCAT to program the PLC 
initially, and to identify all the PDO data which must be coped.

     There is nothing fundamentally difficult about FSoE, except 
understanding how all the pieces fit together is not easy. Suggest 
reading the FSoE specification (ETG5100) first for an overview. The 
specification does not disclose anything about the specific EL6900 
implementation in terms of how to burn your PLC code onto the EL6900 -- 
this is a black box for which TwinCAT is mandatory.

     In every cycle of the domain, the application (your code) must copy 
short byte arrays of data from the PLC TxPDO to each FSoE slave, and 
from each FSoE slave to the PLC. This is easy to arrange with, for 
example, memcpy(). The use of fancy datagram commands like FRMW or 
overlapped mapping of the PDOs in logical space is not at all useful 
with regards to FSoE -- the data movement is simply copying bits between 
ordinarily mapped PDOs in the application software and nothing more. The 
protocol is designed to accept multiple process data cycles of latency 
between updates, as the fault condition is detected using a watchdog timer.

         Best regards - Dave

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