Lake Shore Cryotronics 121, Руководство пользователя

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26 CHAPTER 4: Computer Interface Operation
5. Select Search for the best driver in these locations , click to clear the
Search removable media check box, and click the Include this loca-
tion in the search check box.
6. Click Browse and open the location of the extracted driver.
7. Click Next .
8. When the driver finishes installing a confirmation message stating
“The wizard has finished installing the software for Lake Shore
Model 121 Current Source” should appear. Click
Finish to complete
the installation.
4.2.4 Communication
Communicating via the USB interface is done using message strings. The
message strings should be carefully formulated by the user program
according to some simple rules to establish effective message flow con-
trol.
4.2.4.1 Character Format
A character is the smallest piece of information that can be transmitted
by the interface. Each character is ten bits long and contains data bits,
character timing bits, and an error detection bit. The instrument uses 7
bits for data in the American Standard Code for Information Interchange
(ASCII) format. One start bit and one stop bit are necessary to synchro-
nize consecutive characters. Parity is a method of error detection. One
parity bit configured for odd parity is included in each character.
ASCII letter and number characters are used most often as character
data. Punctuation characters are used as delimiters to separate different
commands or pieces of data. A special ASCII character, line feed (LF 0AH),
is used to indicate the end of a message string. This is called the message
terminator.
4.2.4.2 Message Strings
A message string is a group of characters assembled to perform an inter-
face function. There are three types of message strings: commands, que-
ries and responses. The computer issues command and query strings
through user programs, the instrument issues responses. Two or more
command or query strings can be chained together in one communica-
tion, but they must be separated by a semi-colon (;). The total communi-
cation string must not exceed 255 characters in length.