Instrument Control Toolbox

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 serial port COM1. 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.

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

s = serial('COM1');

2. Connect to the instrument - Connect s to the oscilloscope. Since 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)

3. 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?')
s.BytesAvailable
ans =
    56
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. Since 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)
ptop =
2.0199999809E0

4. 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

Rules for Completing Write and Read Operations

Using Events and Actions