PAM sampling flat-top of an sinus signal

Hi,

i need to do a flat-top PAM sampling of an sinus signal of 800Hz with a sampling frequency of 3000hz. I did natural sampling with this code, but i need it falt-topped, i don't know how to do that... Thanks!

Here is my working code for the natural PAM sampling :

if true
clear all;
close all;
Fs = 1e9;
t = 0:1/Fs:(0.2e-2);
fc = 3000; %sampling frequency
fm = 800; %message frequency
a = 1;
vm = a.*sin(2*pi*fm*t); %message
pulseperiods = [0:10]*0.25e-3;
pulsewidth = (1/fc)/3;
vc = pulstran(t,pulseperiods,@rectpuls,pulsewidth);
y = vc.*vm;
figure
subplot(3,1,1);
plot(t,vm); % plot message
xlabel('Temps');
ylabel('Amplitude');
title('Message');
subplot(3,1,2);
plot(t,vc); % plot pulse 
xlabel('Temps');
ylabel('Amplitude');
title('Switching waveform');
subplot(3,1,3);
plot(t,y); % plot PAM naturel
xlabel('Temps');
ylabel('Amplitude');
title('PAM naturel');

end