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10-3
IM 704610-01E
Communication Command
10
Notes Regarding Sending and Receiving
Messages
• When a program message is sent that does not
contain a query, the next program message can be
sent any time.
• When a program message is sent that contains a
query, a response message must be received
before the next program message can be sent. If a
response message is not received, or only received
in part, an error occurs when the next program
message is sent. Unreceived response messages
are thrown out.
• If the controller attempts to receive a response
message that does not exist, an error occurs. If the
controller tries to receive a response message
before completing the sending of a program
message, an error occurs.
• When sending a program message with multiple
units in the message, if any of the units are
incomplete, the instrument attempts to execute the
program message units it thinks are complete, but
will not necessarily do so successfully. Also, if a
query is included in the units, a response will not
necessarily be returned.
Deadlock Status
This instrument can store messages of at least 1024
bytes (received or sent) in a buffer (the number of
bytes increases or decreases depending on the
operational status). When both the transmit and
receive buffers become full at the same time, the
instrument can no longer continue to operate. This is
called deadlock status. In this situation, operation can
be restored by discarding the response message. If
you keep program messages including to 1024 bytes
or less, deadlock should not occur. Also, deadlock will
not occur if queries are not included in the program
message.
10.1 Program Format
10.1.3
Commands
Commands
There are three types of commands (program headers)
that can be sent from the controller to the instrument.
The format of each kind of header is different.
Common Command Headers
Commands defined in the IEEE 488.2-1987 standard
are called common commands. The following is the
format of common commands. Headers must begin
with an asterisk (
*
).
∗
<Mnemonic>
?
An example of a common command:
*CLS
Compound Header
Instrument-specific commands which are not common
commands are classified by function, and are layered
hierarchically. The following is the format for
compound headers. Sub layers must begin with a
colon (
:
).
:
<Mnemonic>
?
:
An example of a compound header:
MEASURE:FUNCTION
Simple Header
These are functionally independent commands without
sub layers. The following is the format for the simple
header.
<Mnemonic>
?
:
An example of a simple header:
START
Note
The mnemonic is an alphanumeric string.