[etherlab-dev] i met problems when i try to communicate with slaves.

Gavin Lambert gavinl at compacsort.com
Thu Jun 26 01:01:19 CEST 2014

On 25 June 2014, quoth taotao:
> I try to build ethercat on ubuntu. Now Ethercat host master has been 
> successfully established.

These sorts of questions really belong on the users list.

> Q1: How can i find slave's alias and position(ec_slave_config_t)?
> i try to use command "/opt/xxx/ethercat sl -v" , but there not have this information.  

It does.  If you run "ethercat slaves" without the -v, you'll see a number on the left (this is the absolute ring position, starting from 0) and in the second column a N:M pair (this is the relative position from the nearest previous device with an alias; if it's showing :0 then that's the alias for the device itself).

> Q2: If i just have only one slave (ET1100) , so I just one slave's alias and position, 
> I 'm right?
> Example c file always has four defines ( slave's alias and position).

You can address any slave either as "0, absolute" or as "alias, relative".  Both work; which one you use just depends on what the requirements of your application and network configuration are.

> Q3:  struct ec_pdo_entry_reg_t:
> what is slave alias address?   It is xml (beckoff 's slave configure xml) 
> keyword :startaddress?
> what is slave direction? how can it get this information?

No.  You need to specify which PDOs your application is interested in retrieving.  You should already know that from the slave's datasheet, or you can look at the defaults using the "ethercat pdos" command.

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