Lake Shore 370 User Manual

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Lake Shore 370 User Manual Manual pdf 119 page image

Lake Shore Model 370 AC Resistance Bridge User’s ManualMessage Strings (Continued)A query string is issued by the computer and instructs the instrument to send a response. The query format is:.Query mnemonics are often the same as commands with the addition of a question mark. Parameter data is oftenunnecessary when sending queries. Query mnemonics and parameter data if necessary is described in Paragraph 6.3.Terminators must be sent with every message string. The computer should expect a response very soon after a query issent.A response string is the instruments response or answer to a query string. The instrument will respond only to the lastquery it receives. The response can be a reading value, status report or the present value of a parameter. Response dataformats are listed along with the associated queries in Paragraph 6.3. The response is sent as soon as possible after theinstrument receives the query. Typically it takes 10 ms for the instrument to begin the response. Some responses takelonger.6.2.6 Message Flow ControlIt is important to remember that the user program is in charge of the serial communication at all times. The instrumentcan not initiate communication, determine which device should be transmitting at a given time or guarantee timingbetween messages. All of this is the responsibility of the user program.When issuing commands only the user program should:• Properly format and transmit the command including terminators as one string.• Guarantee that no other communication is started for 50 ms after the last character is transmitted.• Not initiate communication more than 20 times per second.When issuing queries or queries and commands together the user program should:• Properly format and transmit the query including terminators as one string.• Prepare to receive a response immediately.• Receive the entire response from the instrument including the terminators.• Guarantee that no other communication is started during the response or for 50 ms after it completes.• 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 intermittentfailures in communication.6.2.7 Serial Interface Example ProgramsA Visual Basic program is included to illustrate the serial communication functions of the instrument. Refer toSection 6.2.7.1 for instructions on how to setup the program. The Visual Basic code is provided in Table 6-8.A description of program operation is provided in Section 6.2.7.2. While the hardware and software required to produceand implement these programs not included with the instrument, the concepts illustrated apply to most applications.Remote Operation 6-13

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