NOTE:
The RS-485 interface in the LiQuilaz II presents a fixed data queue of 10.
Appendix B RS-485 Communication Protocol
LiQuilaz II E and S Operations Manual
Page B-3
The LiQuilaz II will respond with a value of -1 to a CQC command only after a software
reset has occurred. A software reset can occur due to power-up, a CSR command from
the user, or an error detected by the watch-dog interrupt.
Fast Polling
The logical sequence of events while performing the “Fast” data poll is identical to
those for the “Slow” data poll with the following exceptions:
• The address of the instrument, logically combined with the value 80Hex, is
transmitted instead of the CQC command.
• The response to the “Fast” poll command contains the status (sampling or not).
The queue count is used just like it was used in the “Slow” data poll procedure.
NOTE:
The “Fast” poll command is not typically transmitted any faster than 3
times in one second.
Slow Protocol
The Slow protocol general communication procedure has a “command/response
sequence.” For each command directed to a LiQuilaz II Liquid Particle Counter, a
response is generated by the unit. The format of the response depends on the
particular command. See Slow Protocol Commands on page
B-5 for a complete listing
of the LiQuilaz II Liquid Particle Counter commands. These commands and responses
are formatted and packeted to ensure error-free communication. The formatting and
packeting process is discussed in the following paragraphs.
The process of building a packet can be divided into three logical steps as described
below.
First Logical Step
The address of the node is added to the beginning of the data, and a checksum is
added to the end of the data. This produces the following
un-formatted data structure.
ADDRESS HIGH BYTE|ADDRESS LOW BYTE|FIRST DATA BYTE|SECOND DATA
BYTE|...|LAST DATA BYTE|CHECKSUM HIGH BYTE|CHECKSUM LOW BYTE
NOTE:
CHECKSUM is a 16-bit unsigned integer sum of the unformatted data
including the address with the carry bit ignored, if an overflow occurs
during the calculation. STX and ETX are not included in the check sum.
NOTE:
“|” is used for readability and does not exist in the actual data packet.
