Flachmann und Heggelbacher Docklight V2.2, User Manual

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Docklight V2.2 User Manual 07/2016 Copyright 2016 Flachmann und Heggelbacher GbR
Glossary / Terms Used
11 Glossary / Terms Used
11.1 Action
For a Receive Sequence, the user may define an action that is performed after receiving
the specified sequence. Possible actions are
· Sending a Send Sequence
Only Send Sequences without any wildcards can be used
· Inserting a comment
A user-defined text or an additional date/time stamp is added to the communication
data window and log file
· Triggering a Snapshot
· Stopping communication
11.2 Break
A break state on an RS232 connection is characterized by the TX line going to Space
(logical 0) for a longer period than the maximum character frame length including start
and stop bits. Some application protocols, e.g.
LIN , use this for synchronization
purposes.
11.3 Character
A character is the basic unit of information processed by Docklight. Docklight always
uses 8 bit characters. Nevertheless, the communication settings also allow data
transmission with 7 bits or less. In this case, only a subset of the 256 possible 8 bit
characters will be used but the characters will still be stored and processed using an 8
bit format.
11.4 CRC
Cyclic Redundancy Code. A CRC is a method to detect whether a received sequence/
message has been corrupted, e.g. by transmission errors. This is done by constructing
an additional checksum value that is a function of the message data, and then
appending this value to the original message. The receiver calculates the checksum from
the received data and compares it to the transmitted CRC value to see if the message is
unmodified. CRCs are commonly used because they allow the detection of typical
transmission errors (bit errors, burst errors) with a very high accuracy.
CRC algorithms are based on polynomial arithmetic, and come in many different
versions. Common algorithms are CRC-CCITT, CRC-16 and CRC-32. An example of an
application protocol that uses a CRC is
MODBUS over Serial Line .
A very popular article about CRCs is "Easier said than done (Michael Barr) - A guide to
CRC calculation":
http://www.netrino.com/Connecting/2000-01/
Docklight Scripting's CRC functionality (DL.CalcChecksum) was inspired by the above
article and the proposed Boost CRC library:
http://www.boost.org/libs/crc/index.html