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6:
Computer Interface Operation
Model 372 AC Resistance Bridge and Temperature Controller
A query string is issued by the computer and instructs the instrument to send a
response. The query format is:
<query mnemonic><?><space><parameter data><terminators>.
Query mnemonics are often the same as commands with the addition of a question
mark. Parameter data is often unnecessary when sending queries. Query mnemonics
and parameter data if necessary is described in section 6.6. Terminators must be sent
with every message string. The computer should expect a response very soon after a
query is sent.
A response string is the instrument’s response or answer to a query string. The
response can be a reading value, status report or the present value of a parameter.
Response data formats are listed along with the associated queries in section 6.6. The
response is sent as soon as possible after the instrument receives the query.
6.3.5 Message Flow
Control
It is important to remember that the user program is in charge of the USB communi-
cation at all times. The instrument cannot initiate communication, determine which
device should be transmitting at a given time, or guarantee timing between mes-
sages. All of this is the responsibility of the user program.
When issuing commands the user program alone should:
D
Properly format and transmit the command including the terminator as 1 string
D
Guarantee that no other communication is started for 50 ms after the last char-
acter is transmitted
D
Not initiate communication more than 20 times per second
When issuing queries or queries and commands together, the user program should:
D
Properly format and transmit the query including the terminator as 1 string
D
Prepare to receive a response immediately
D
Receive the entire response from the instrument including the terminator
D
Guarantee that no other communication is started during the response or for
50 ms after it completes
D
Not initiate communication more than 20 times per second
Failure to follow these simple rules will result in inability to establish communication
with the instrument or intermittent failures in communication.
6.4 Ethernet
Interface
The Ethernet interface provides a means of connecting the Model 372 to an Ethernet
based computer network. Ethernet networks provide the ability to communicate
across large distances, often using existing equipment (the internet, pre-existing
local networks). The Ethernet interface of the Model 372 provides the ability to use
TCP socket connections (section 6.4.3) to send commands and queries to the instru-
ment using the common command set detailed in section 6.6. The Model 372 has an
embedded web interface that provides status information and additional utilities
(section 6.5).
Menu navigation:
Interface
Q
Enabled
Q
Ethernet
6.4.1 Ethernet
Configuration
There are several parameters for configuring the Model 372 Ethernet interface and
three methods for configuring these parameters. This section contains a brief expla-
nation of each of these. A comprehensive discussion of computer networking is
beyond the scope of this manual. These settings may depend on your network config-
uration; contact your network administrator for assistance.