Example: Writing and Reading Text Data :: Serial Port I/O (External Interfaces)

External Interfaces

Example: Writing and Reading Text Data

This example illustrates how to communicate with a serial port instrument by writing and reading text data.

The instrument is a Tektronix TDS 210 two-channel oscilloscope connected to the COM1 port. Therefore, many of the commands given below are specific to this instrument. A sine wave is input into channel 2 of the oscilloscope, and your job is to measure the peak-to-peak voltage of the input signal.

Create a serial port object - Create the serial port object s associated with serial port COM1.

```
s = serial('COM1');
```

Connect to the device - Connect s to the oscilloscope. Because the default value for the ReadAsyncMode property is continuous, data is asynchronously returned to the input buffer as soon as it is available from the instrument.

```
fopen(s)
```

Write and read data - Write the *IDN? command to the instrument using fprintf, and then read back the result of the command using fscanf.

fprintf(s,'*IDN?')
idn = fscanf(s)
idn =
TEKTRONIX,TDS 210,0,CF:91.1CT FV:v1.16 TDS2CM:CMV:v1.04

You need to determine the measurement source. Possible measurement sources include channel 1 and channel 2 of the oscilloscope.
- ```
fprintf(s,'MEASUREMENT:IMMED:SOURCE?')
source = fscanf(s)
source =
CH1
```
The scope is configured to return a measurement from channel 1. Because the input signal is connected to channel 2, you must configure the instrument to return a measurement from this channel.
- ```
fprintf(s,'MEASUREMENT:IMMED:SOURCE CH2')
fprintf(s,'MEASUREMENT:IMMED:SOURCE?')
source = fscanf(s)
source =
CH2
```
You can now configure the scope to return the peak-to-peak voltage, and then request the value of this measurement.
- ```
fprintf(s,'MEASUREMENT:MEAS1:TYPE PK2PK')
fprintf(s,'MEASUREMENT:MEAS1:VALUE?')
```
Transfer data from the input buffer to MATLAB using fscanf.
- ```
ptop = fscanf(s,'%g')
ptop =
2.0199999809E0
```

Disconnect and clean up - When you no longer need s, you should disconnect it from the instrument, and remove it from memory and from the MATLAB workspace.

```
fclose(s)
delete(s)
clear s
```

Reading Data Example: Parsing Input Data Using strread