This demo explores asynchronous read and write operations using a TCPIP object.
The information obtained for this demonstration was prerecorded. Therefore, you do not need an actual instrument to learn about asynchronous TCPIP read and write operations. The instrument used was a SONY/TEKTRONIX AWG520 Arbitrary Waveform Generator.
These functions are associated with reading and writing text asynchronously:
FPRINTF - Write text to instrument. READASYNC - Asynchronously read bytes from an instrument. STOPASYNC - Stop an asynchronous read and write operation.
These properties are associated with ASCII read and write asynchronous operations:
BytesAvailable - Indicate the number of bytes available in
the input buffer.
TransferStatus - Indicate what type of asynchronous operation
is in progress.
ReadAsyncMode - Specify whether data is read continuously
in the background or whether you must call
the READASYNC function to read data
asynchronously.Additionally, you can use all callback properties during asynchronous read and write operations.
The object can operate in synchronous mode or in asynchronous mode. When the object is operating synchronously, the read and write routines block the MATLAB command line until the operation has completed or a timeout occurs. When the object is operating asynchronously, the read and write routines return control immediately to the MATLAB command line.
Additionally, you can use callback properties and callback functions to perform tasks as data is being written or read. For example, you can create a callback function that notifies you when the read or write operation has finished.
To begin, create a TCPIP object associated with the address sonytekawg.mathworks.com, port 4000. The instrument's host IP address, e.g. 192.168.1.10, is user-configurable in the instrument. The associated host name is given by your network administrator. The port number is fixed and is found in the instrument's documentation.
>> t = tcpip('sonytekawg.mathworks.com', 4000);
>> tTCPIP Object : TCP/IP- sonytekawg.mathworks.com
Communication Settings
RemotePort: 4000
RemoteHost: sonytekawg.mathworks.com
Terminator: 'LF' Communication State
Status: closed
RecordStatus: off Read/Write State
TransferStatus: idle
BytesAvailable: 0
ValuesReceived: 0
ValuesSent: 0Before you can perform a read or write operation, you must connect the TCPIP object to the instrument with the FOPEN function. If the TCPIP object was successfully connected, its Status property is automatically configured to open.
>> fopen(t) >> get(t, 'Status')
ans =
open
You can read data asynchronously with the TCPIP object in one of these two ways:
The FSCANF, FREAD, FGETL and FGETS functions are used to bring the data from the input buffer into MATLAB. These functions operate synchronously.
To begin, lread data continuously.
>> set(t, 'ReadAsyncMode', 'continuous')
Now, query the instrument for the SCPI version number.
>> fopen(t); >> fprintf(t, 'SYSTEM:VERSION?')
Because the ReadAsyncMode property is set to 'continuous', the object is continuously asking the instrument if any data is available. Once the last FPRINTF function completes, the instrument begins sending data, the data is read from the instrument and is stored in the input buffer.
>> get(t, 'BytesAvailable')
ans =
7
You can bring the data from the object's input buffer into the MATLAB workspace with FSCANF.
>> SCPIversion = fscanf(t)
SCPIversion =
1995.0
Next, read the data manually.
>> set(t, 'ReadAsyncMode', 'manual')
Now, query the instrument for the elapsed time since powerup.
>> fprintf(t, 'SYSTEM:UPTIME?')
Once the last FPRINTF function completes, the instrument begins sending data. However, because ReadAsyncMode is set to manual, the object is not reading the data being sent from the instrument. Therefore no data is being read and placed in the input buffer.
>> get(t, 'BytesAvailable')
ans =
0
The READASYNC function can asynchronously read the data from the instrument. The READASYNC function returns control to the MATLAB command line immediately.
The READASYNC function takes two input arguments. The first argument is the instrument object and the second argument is the SIZE, the amount of data to be read from the instrument.
The READASYNC function without a SIZE specified assumes SIZE is given by the difference between the InputBufferSize property value and the BytesAvailable property value. The asynchronous read terminates when
An error event will be generated if READASYNC terminates due to a timeout.
The object starts querying the instrument for data when the READASYNC function is called. Because all the data was sent before the READASYNC function call, no data will be stored in the input buffer and the data is lost.
>> readasync(t); >> get(t, 'BytesAvailable')
ans =
0
When the TCPIP object is in manual mode (the ReadAsyncMode property is configured to manual), data that is sent from the instrument to the computer is not automatically stored in the input buffer of the TCPIP object. Data is not stored until READASYNC or one of the blocking read functions is called.
Manual mode should be used when a stream of data is being sent from your instrument and you only want to capture portions of the data.
Now, configure our TCPIP object to notify us when a terminator has been read.
>> set(t, 'ReadAsyncMode', 'continuous')
>> set(t, 'BytesAvailableFcn', {'dispcallback'})Note, the default value for the BytesAvailableFcnMode property indicates that the callback function defined by the BytesAvailableFcn property will be executed when the terminator has been read.
>> get(t, 'BytesAvailableFcnMode')
ans =
terminator
The M-file callback function DISPCALLBACK is defined below.
function dispcallback(obj, event) %DISPCALLBACK Display event information for the specified event. % % DISPCALLBACK(OBJ, EVENT) a callback function that displays % a message which contains the type of the event, the name % of the object which caused the event to occur and the % time the event occurred. % % See also INSTRCALLBACK.
callbackTime = datestr(datenum(event.Data.AbsTime)); fprintf(['A ' event.Type ' event occurred for ' obj.Name ' at ' callbackTime '.\n']);
Now, query the instrument for the LAN address. Once the terminator is read from the instrument and placed in the input buffer, DISPCALLBACK is executed and a message is posted to the MATLAB command window indicating that a BytesAvailable event occurred.
>> fprintf(t, 'syst:comm:lan:addr?')
A BytesAvailable event occurred for TCP/IP-sonytekawg.mathworks.com at 21-Jan-2002 17:53:35.
>> get(t, 'BytesAvailable')
ans =
18
>> data = fscanf(t, '%c', 18)
data =
"144.212.113.249"
Note: the last value read is the line feed (10):
>> real(data)
ans =
Columns 1 through 15
34 49 52 52 46 50 49 50 46 49 49 51 46 50 52
Columns 16 through 18
57 34 10
Now suppose that halfway through the asynchronous read operation, you realize that the data being read from the instrument was incorrect. Rather than waiting for the asynchronous operation to complete, you can use the STOPASYNC function to stop the asynchronous read. Note that if an asynchronous write was in progress, the asynchronous write operation would also be stopped.
>> get(t, {'TransferStatus','BytesAvailable'})ans =
'read' [125]
>> stopasync(t);
>> get(t, {'TransferStatus', 'BytesAvailable'})ans =
'idle' [165]
The data that has been read from the instrument remains in the input buffer. You can use one of the synchronous read functions to bring this data into the MATLAB workspace. However, because this data represents the wrong data, the FLUSHINPUT function is called to remove all data from the input buffer.
>> flushinput(t);
>> get(t, {'TransferStatus', 'BytesAvailable'});ans =
'idle' [0]
You can perform an asynchronous write with the FPRINTF or FWRITE functions by passing 'async' as the last input argument.
In asynchronous mode, you can use callback properties and callback functions to perform tasks while data is being written. For example, configure the object to notify us when an asynchronous write operation completes.
>> set(t, 'OutputEmptyFcn', {'dispcallback'});
>> fprintf(t, 'syst:comm:lan:addr?', 'async')A OutputEmpty event occurred for TCP/IP-sonytekawg.mathworks.com at 21-Jan-2002 18:03:05. A BytesAvailable event occurred for TCP/IP-sonytekawg.mathworks.com at 21-Jan-2002 18:03:05.
If the STOPASYNC function is called during an asynchronous write operation, the asynchronous write will be stopped and the data in the output buffer will automatically be flushed. If an asynchronous read operation was also in progress, it would also be stopped. However, the data in the input buffer would not be flushed automatically.
If you are finished with the TCPIP object, disconnect it from the instrument, remove it from memory, and remove it from the workspace.
>> fclose(t); >> delete(t); >> clear t