Vector Error

I am trying to read data from a serial port and store the values in a vector to eventually plot.

I keep getting the following error:

"In an assignment A(I) = B, the number of elements in B and I must be the same."

I understand that the data from the serial port may not be the same size, but I cannot figure out how to remedy this problem. Here is the basic program that I am testing with:

for i = 1 : 10

    y(i) = fread(s) 
end

I am also just using Hyperterminal to test.

Any help is much appreciated!

Answer 1

[David Young]

A call to fread returns a vector, but you can only store a single number in y(i) if i is a scalar (which it is in your code - i is one of the numbers from 1 to 10).

The solution really depends on what you want to do with the data afterwards, but one possibility is to store each vector in one element of a cell array. To do this, you'd replace the second line of your code with

y{i} = fread(s);

(You could also preallocate y before the loop, using

y = cell(1, 10);

)

This keeps the data from each call to fread separate.

If you want to combine the vectors into one big vector, you can do

y = [];
for i = 1:10
  y = [y; fread(s)];
end

You may well need to make your code more complex in order to read successfully from the serial port - for example, you may need to test BytesAvailable(s) to see whether to continue the loop or pause.

[Walter Roberson]

Note: fread() applied to a serial port will read until the end of the defined InputBufferSize unless it gets an error or timeout.

If you want to read only 1 byte, specify the size

fread(s,1)

Answer 2

[Steve]

Awesome. Thanks guys!!