User manual

IEC61131 User and Reference Manual
April 22, 2008
453
Data Link Layer
The data link layer handles the transmission and reception of data frames across the physical layer.
Each data link frame contains a source and destination address to ensure the receiving device knows
where to send the response. To ensure data integrity data link layer frames contain two CRC bytes
every 16 bytes.
Data link layer frames are sent with or without a confirmation request. When a confirmation is
requested the receiving device replies with a confirmation indicating the message was received and
the CRC checks passed.