capacitor plot charging and discharging for 555 astable multivibrator

Hi guys

I want to plot the waveform for vc for an astable multivibrator. The problem is that the graph should be surrounded by (1/3 and 2/3) from the voltage source. Another problem is that for some resistors values the plot is weird. I will the function code and some plots

function vcplot_Callback(hObject, eventdata, handles)

ra = str2num(get(handles.edit1,'string'));

rb = str2num(get(handles.edit2,'string'));

c = str2num(get(handles.edit3,'string'))/1000000;

vcc = str2num(get(handles.edit4, 'string'));

tc = 0.69*(ra+rb)*c;

td = 0.69* rb*c;

t = 0.693*(ra+(2*rb))*c;

d = (tc/t)*100; % duty cycle

[v1, t1] = vcfunction(vcc, ra, rb,c);

figure(1);

m=5; % Repetition

n=numel(t1);

tt=0:0.01:n*m*0.01-0.01;

vv=repmat(v1,1,m);

plot(tt,vv)

grid on

% Add labels

ylim([-15 15]);

xlabel('Time(s)')

ylabel('Amplitude(V)')

title('Waveform of 555 Timer as an Astable Multivibrator')