How to take frequency samples and time interval to plot fft in MATLAB?

Hello,

i have a vector containing 2048 data(ASCII file) in this manner like [87 92 80 45 .... ]. I want to plot fft of this data. So I just want to know how to take frequency sample and time interval to plot fft of this data? I wrote the following code to calculate fft of this code. Please suggest whether the frequency sample and time interval is right or wrong? or suggest the code to calculate fft of this data.

I = load('data1.asc');

for i = 1:2048

x = I(:,2);

end

plot(x)

*Fs = 40000; * Frequency Samples

*T = 1/Fs; * Time

L = 2000;

NFFT = 2^nextpow2(L);

Y = abs(fft(x,NFFT))/L;

f = Fs/2*linspace(0,1,NFFT/2+1);

figure, plot(f,2*abs(Y(1:NFFT/2+1)))

axis([0 40000 0 40])

xlabel('Frequency (Hz)')

ylabel('|Y(f)|')