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query

Write text to instrument, and read data from instrument

Syntax

out = query(obj,'cmd')
out = query(obj,'cmd','wformat')
out = query(obj,'cmd','wformat','rformat')
[out,count] = query(...)
[out,count,msg] = query(...)
[out,count,msg,datagramaddress,datagramport] = query(...)

Arguments

obj

An interface object.

'cmd'

String that is written to the instrument.

'wformat'

Format for written data.

'rformat'

Format for read data.

out

Contains data read from the instrument.

count

The number of values read.

msg

A message indicating if the read operation was unsuccessful.

datagramaddress

The datagram address.

datagramport

The datagram port.

Description

out = query(obj,'cmd') writes the string cmd to the instrument connected to obj. The data read from the instrument is returned to out. By default, the %s\n format is used for cmd, and the %c format is used for the returned data.

out = query(obj,'cmd','wformat') writes the string cmd using the format specified by wformat.

wformat is a C language conversion specification. Conversion specifications involve the % character and the conversion characters d, i, o, u, x, X, f, e, E, g, G, c, and s. Refer to the sprintf file I/O format specifications or a C manual for more information.

out = query(obj,'cmd','wformat','rformat') writes the string cmd using the format specified by wformat. The data read from the instrument is returned to out using the format specified by rformat.

rformat is a C language conversion specification. The supported conversion specifications are identical to those supported by wformat.

[out,count] = query(...) returns the number of values read to count.

[out,count,msg] = query(...) returns a warning message to msg if the read operation did not complete successfully.

[out,count,msg,datagramaddress,datagramport] = query(...) returns the remote address and port from which the datagram originated. These values are returned only when using a UDP object.

Examples

This example creates the GPIB object g, connects g to a Tektronix® TDS 210 oscilloscope, writes and reads text data using query, and then disconnects g from the instrument.

g = gpib('ni',0,1);
fopen(g)
idn = query(g,'*IDN?')
idn =
TEKTRONIX,TDS 210,0,CF:91.1CT FV:v1.16 TDS2CM:CMV:v1.04
fclose(g)

More About

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Tips

Before you can write or read data, obj must be connected to the instrument with the fopen function. A connected interface object has a Status property value of open. An error is returned if you attempt to perform a query operation while obj is not connected to the instrument.

query operates only in synchronous mode, and blocks the command line until the write and read operations complete execution.

Using query is equivalent to using the fprintf and fgets functions. The rules for completing a write operation are described in the fprintf reference pages. The rules for completing a read operation are described in the fgets reference pages.

See Also

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