PWM and serial communication

Hi,

i wish to communicate with mcu ATmega128 with PWM. I used to program the PWM pulse by setting the timer 0 and the mcu PWM port.

In Matlab, may i know how the PWM is generated, after i had the serial communication with the mcu code:

s=serial('COM6');
fopen(s);
fwrite(s,170,'unit8');
fwrite(s,170,'unit8');
fwrite(s,85,'unit8');
fwrite(s,85,'unit8');
fwrite(s,value,'unit8');
fwrite(s,value,'unit8');
fclose(s);
delete(s);

Besides, there's 1 more problem when I'm using fscanf(s,'*IDN?'), it show empty array and timer out because it can't reach the terminator. Is there any wrong in my code? Thanks. Your help is much appreciate.