Your code is not correct. Plus, generating a puls train with Matlab function is not a good idea. You have to know that your Matlab function block, the way it's programmed, will outpu,t each sample time, an entire array.
You can generate such signal with from file block, from worksapce block or using repeated sequence
If you want to use from file block
Fs=1e+9
tend=10*4e-6
t=0:1/Fs:tend;
pulsewidth=1e-6
pulseperiods=(0:10)*4e-6
x=pulstran(t,pulseperiods,'rectpuls',pulsewidth)
v=[t;x];
save yourfile v
Then set the name "yourfile" in the frome file block
