[etherlab-users] PDO entry bit length

Florian Pose fp at igh-essen.com
Mon Jul 6 11:00:05 CEST 2009


On Fri, Jul 03, 2009 at 11:08:04AM +0200, amazue wrote:
> We use version 1.5.0 of IgH EtherCAT Master with a Hilscher CiFX Slave.
> By default, this slave provides in input only one PDO containing a
> unique 200-bytes entry, and the same thing in output.
> 
> The problem is that the bit_length of ec_pdo_entry_inf_t is only a
> uint8_t, making us unable to declare our 1600 bits.

The reason is that the PDO Entry bit length is defined as Unsigned8 in
the EtherCAT specification, see. the *PDO SII categories (AL spec. table
25) and also when setting/reading the PDO Entry mapping via CoE. Thus,
using a bit length > 255 is not possible in this way. The PDO entries
can be separated to smaller units.

> Does Hilscher product match with EtherCAT standards ?

Generally spoken: Yes. It they allow you to change the PDO mapping to
smaller units, it's okay. But I wonder, why the do not warn about
this...

-- 
Best regards,
Florian Pose

http://etherlab.org



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