Arduino serial connection reading in data only until buffer is full

I am trying to use an Arduino to read in sensor data into MATLAB and store it. I am using a relatively high baud rate (57600) and the MATLAB buffer keeps filling up, causing small lags in my data. I would like to be able to just read in the data until the buffer is full and then stop. I know you can set the input buffer size but is there any way to open/close the buffer or stop the data collection once I have read in a specific number of bytes? I know I can set the amount of time or number of characters to read in before stopping but I need to be able to specify the number of bytes. For example, I know the default buffer size is 512 bytes, so how would I be able to read in exactly 512 bytes and then stop? I am currently using fscanf to read in the data from the Arduino through a serial port. I haven't had any luck so far and would appreciate some guidance.

Answer 1

[Walter Roberson]

inbytes = char(fread(s, 512));

and then you can sscanf on inbytes to extract the printable data.