6.3.4 Communication
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c. In the main window of Device Manager, locate the
Ports
(COM & LPT)
device type. In many instances this will be between the Network adapt-
ers and Processors items. If the
Ports
(COM & LPT) item is not already
expanded, click the + icon. Lake Shore Model 372 should appear
indented underneath
Ports
(COM & LPT). If it is not displayed as
Lake Shore Model 372, it might be displayed as USB Device. If neither are
displayed, click
Action
and then select
Scan for hardware changes
,
which may open the Found New Hardware wizard automatically. If the
Found New Hardware wizard opens, continue to step 4.
d. Right-click on Lake Shore Model 372 and click
Update Driver
.
4. Select
No, not at this time
and click
Next
.
5. Select
Search for the best driver in these locations
, click to clear the
Search
removable media
check box, and click the
Include this location 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 372 AC Resistance
Bridge and Temperature Controller” should appear. Click
Finish
to complete the
installation.
6.3.4 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 control.
6.3.4.1 Character Format
A character is the smallest piece of information that can be transmitted by the inter-
face. Each character is ten bits long and contains data bits, bits for character timing,
and an error detection bit. The instrument uses seven bits for data in the American
Standard Code for Information Interchange (ASCII) format. One start bit and one stop
bit are necessary to synchronize 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. Punctua-
tion 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 mes-
sage string. This is called the message terminator. The Model 372 will accept either
the line feed character alone, or a carriage return (CR 0DH) followed by a line feed as
the message terminator. The instrument query response terminator will include both
carriage return and line feed.
6.3.4.2 Message Strings
A message string is a group of characters assembled to perform an interface function.
There are three types of message strings: commands, queries, 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 communication, but they must be separated by a semi-colon (;). The total com-
munication string must not exceed 255 characters in length.
A command string is issued by the computer and instructs the instrument to perform
a function or change a parameter setting. The format is:
<command mnemonic><space><parameter data><terminators>.
Command mnemonics and parameter data necessary for each one is described in
section 6.6. Terminators must be sent with every message string.