Problem with the number of successive serial commands (fprintf())

Hi,

I am having a problem with the number of successive serial commands (fprintf())sent through a USB serial port. I am doing a project where I have to send a number of commands to move two stepper motors into specified coordinates. The motion controller I am using is a JAF motion controller (<http://www.jafmotion.co.uk/)>.

The code below is executed after pressing a button on a MATLAB GUI:

if true
  s = serial(‘COM4′);
  fopen(s);
  fprintf(s, '-3262 -1920;');
  fprintf(s,'PD4000;');
  fprintf(s, '-5234 -1231;');
  fprintf(s,'PD4000;');
  fprintf(s, '-5123 -5122;');
  fprintf(s,'PD4000;');
  fprintf(s, '-9872 -1221;');
  fprintf(s,'PD4000;');
  fprintf(s, '-5123 -7272;');
  fprintf(s,'PD4000;');
  ...
  fclose(s);
end

The numbers inside the brackets are the coordinate system specified by JAF.

The problem is that the stepper motors only move to a particular point (Say -5123, -5122) and then stop. Any number of successive fprintf() commands below 16 seem to work but any fprintf() statements after the 16th one don't do anything.

I am pretty sure this is a software problem, not hardware. I have tried changing the input and output buffer sizes to 1024 (default is 512) but no effect.

Any ideas why this is happening?

Thanks a lot !

Regards,

Mo