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7. COmmUNICATION PROTOCOL
7.1 Communication interfaces
for firmware versions 1.23 … 1.24
Communication with the thermometer can be implemented using RS232 (baud rate =
9600, data bits = 8, parity = none, stop bits = one, handshaking = none) or USB 2.0 interfa-
ce. USB protocol works as a virtual COM port, and uses the STM Virtual COM Port drivers.
7.2 SCPI protocol
An IEEE-488.2-based protocol is used to communicate with the thermometer, implemen-
ting SCPI commands.
7.2.1 Syntax
Commands consist of ASCII characters, mostly letters and digits, but there are also some
special purpose characters. More details further in this document.
7.2.2 Commands
Commands are individual words, which describe the purpose of performed function. It is
possible to send full words, as well as their mnemonics (up to 4 characters long, abbrevia-
ting its full command, e.g. MEASURE and MEAS). Both, commands and their mnemonics
are unique.
The device should properly respond only on mnemonic or its corresponding full word.
Therefore MEAS, MEASURE, but also MEASUR or MEASURE1 will execute the same
command. Using mnemonics is recommended, since not all full names are properly recog-
nized.
Character case in command is ignored, but this document will tend to use upper-case for
mnemonic, and the rest of full word with lower-case (e.g. MEASure).
7.2.3 Command termination character
Standard program message terminator used, is the new line character (<nl> - 0x0A).
Thermometer recognizes any character lower than space (0x00 – 0x1F) as a message
terminator. End of thermometer’s response is signed with 0x0D, 0x0A (carriage return and
new line). It is possible to send a sequence of commands in a single message, separating
them by semicolon. In such case, thermometer also responds with a sequence, separated
with commas, too. Input and output buffers are 250 characters long.
7.2.4 Structure of commands
Set of commands has a tree structure. It composes of main commands’ catalogues and
their sub-commands. To access specific functions, a full path of commands must be provi
-
ded, where subsequent tree-levels are separated with colon. Having such exemplary tree
of catalogues:
:MEASure
:TEMPerature
:VALue
:GRADient
:RESistance
Summary of Contents for LDT 2000
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Page 14: ...14 5 Typical performance of the thermometer...
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