Read binary data from instrument
A = fread(obj)
A
= fread(obj,size)
A = fread(obj,size,'precision')
[A,count] = fread(...)
[A,count,msg] = fread(...)
[A,count,msg,datagramaddress] = fread(obj,...)
[A,count,msg,datagramaddress,datagramport]
= fread(obj,...)
| An interface object. |
| The number of values to read. |
| The number of bits read for each value, and the interpretation of the bits as character, integer, or floating-point values. |
| Binary data returned from the instrument. |
| The number of values read. |
| A message indicating if the read operation was unsuccessful. |
| The address of the datagram sender. |
| The port of the datagram sender. |
A = fread(obj) and
A
= fread(obj,size) read binary data from the instrument
connected to obj, and returns the data to A.
The maximum number of values to read is specified by size. If
size is not specified, the maximum number of values to read
is determined by the object's InputBufferSize property. Valid
options for size are:
| Read at most |
| Read at most m–by–n values filling an m–by–n matrix in column order. |
size cannot be inf, and an error is returned
if the specified number of values cannot be stored in the input buffer. You specify
the size, in bytes, of the input buffer with the
InputBufferSize property. A value is defined as a byte
multiplied by the precision (see below).
If obj is a UDP object and
DatagramTerminateMode is off, the
size value is honored. If size is less
than the length of the datagram, only size values are read. If
size is greater than the length of the datagram, a warning is
issued stating that a complete datagram was read before size
values was reached.
A = fread(obj,size,'
reads binary data with precision specified by precision')precision.
precision controls the number of bits read for each
value and the interpretation of those bits as integer, floating-point, or character
values. If precision is not specified,
uchar (an 8-bit unsigned character) is used. By default,
numeric values are returned in double-precision arrays. The supported values for
precision are listed below in Tips.
[A,count] = fread(...) returns the number
of values read to count.
[A,count,msg] = fread(...) returns a
warning message to msg if the read operation was
unsuccessful.
[A,count,msg,datagramaddress] = fread(obj,...)
returns the datagram address to datagramaddress if
obj is a UDP object. If more than one datagram is read,
datagramaddress is ' '.
[A,count,msg,datagramaddress,datagramport]
= fread(obj,...)
returns the datagram port to datagramport if
obj is a UDP object. If more than one datagram is read,
datagramport is [ ].
Before you can read data from the instrument, it must be connected to
obj 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 read
operation while obj is not connected to the instrument.
If msg is not included as an output argument and the read
operation was not successful, then a warning message is returned to the command
line.
The ValuesReceived property value is increased by the number
of values read, each time fread is issued.
Note
To get a list of options you can use on a function, press the Tab key after entering a function on the MATLAB® command line. The list expands, and you can scroll to choose a property or value. For information about using this advanced tab completion feature, see Using Tab Completion for Functions.
A read operation with fread blocks access to the
MATLAB Command Window until
The specified number of values is read. For UDP objects,
DatagramTerminateMode must be
off.
The time specified by the Timeout property
passes.
A datagram is received (for UDP objects only when
DatagramTerminateMode is
on).
The input buffer is filled.
The EOI line is asserted (GPIB and VXI instruments only).
The EOSCharCode is received (GPIB and VXI
instruments only).
The EOSCharCode property value is recognized only when
the EOSMode property is configured to
read or read&write. For example,
if EOSMode is configured to read and
EOSCharCode is configured to LF, then
one of the ways that the read operation terminates is when the line feed
character is received.
If EOSMode is none or
write, then there is no terminator defined for read
operations. In this case, fread will complete execution and
return control to the command when another criterion, such as a timeout, is
met.
The supported values for precision are listed
below.
Data Type | Precision | Interpretation |
|---|---|---|
Character |
| 8-bit unsigned character |
| 8-bit signed character | |
| 8-bit signed or unsigned character | |
Integer |
| 8-bit integer |
| 16-bit integer | |
| 32-bit integer | |
| 8-bit unsigned integer | |
| 16-bit unsigned integer | |
| 32-bit unsigned integer | |
| 16-bit integer | |
| 32-bit integer | |
| 32- or 64-bit integer | |
| 16-bit unsigned integer | |
| 32-bit unsigned integer | |
| 32- or 64-bit unsigned integer | |
Floating-point |
| 32-bit floating point |
| 32-bit floating point | |
| 32-bit floating point | |
| 64-bit floating point | |
| 64-bit floating point |