Omega Model CYD211 User’s Manual
4-4 Remote
Operation
Message Strings (Continued)
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
are listed in Paragraph 4.2. Parameters necessary for each one are described
in Paragraph 4.2.1. Terminators must be sent with every message string.
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 are listed in
Paragraph 4.2. Parameter data if necessary is described in Paragraph 4.2.1.
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 instruments 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 Paragraph 4.2.1. The response is sent as soon as possible after the
instrument receives the query. Typically it takes 10 ms for the instrument to
begin the response. Some responses take longer.
4.1.5
Message Flow Control
It is important to remember that the user program is in charge of the serial
communication at all times. The instrument can not initiate communication,
determine which device should be transmitting at a given time, or guarantee
timing between messages. 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.
