| Instrument Control Toolbox | |
Read binary data from the instrument
Syntax
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,...)
Arguments
Description
A = fread(obj,size)
reads 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. Valid options for size are
n |
Read at most n values into a column vector. |
[m,n] |
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 Remarks.
[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 [ ].
Remarks
Before you can read data from the instrument, it must be connected to obj with the fopen function. A connected instrument 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.
Rules for Completing a Binary Read Operation
A read operation with fread blocks access to the MATLAB command line until
DatagramTerminateMode must be off.
Timeout property passes.
DatagramTerminateMode is on).
EOSCharCode is received (GPIB and VXI instruments only).
More About the GPIB and VXI Terminator
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.
Supported Precisions
The supported values for precision are listed below.
Functions
fgetl, fgets, fopen, fscanf, instrhelp
Properties
BytesAvailable, InputBufferSize, Status, ValuesReceived
| | fprintf | freeserial | |