[etherlab-users] EtherCAT datagram size

[Mladen Knezic]

> - The size of the EtherCAT frame is not fixed, i.e. when running and 
> capturing 
> with wireshark, after every "reasonable" frame (the frames which I 
> configured 
> the bytes in), there's a frame with a added 14-byte datagram whose command 
> is 
> 'FPRD' (Configured Address Physical Read ). This makes me confused. Can 
> anyone 
> explain for me?

FPRD command is probably used for some kind of configuration (or diagnostic) 
in system. Can you provide some wireshark capture file or some detailed 
information (e.g. which ESC register is accessed by FPRD command)? From above 
one can conclude that one 16-bit ESC register is read using this command 
(10+2 bytes datagram header (with working counter) and 2 bytes for reading 
register value).

> - The EL2262 takes 7bytes in the PDO. I don't understand why this takes so 
> much 
> space? It has only two outputs, and I used only:
> const static ec_pdo_entry_reg_t domain_regs[] = {     
>    { EL2262SlavePos, Beckhoff_EL2262, 0x7000, 0x01, &off_dig_out1},         
>      {}
> };

EL2262 is XFC terminal, which means that it supports oversampling technique. 
This further means that it may send multiple samples within on EtherCAT 
datagram. That could be answer to your question. Without details about EL2262 
configuration (e.g. oversampling factor) one cannot make any other conclusion.

You can consult the details about the product at the following link:
http://www.beckhoff.com/english.asp?ethercat/el2262.htm

Regards,

--
Mladen Knezic, MSc. E. E.
Research and Teaching Assistant
Faculty of Electrical Engineering
Banja Luka, Bosnia and Herzegovina
Web: www.etfbl.net