How do I acquire multiple datasets using readwrite?

I am trying to record multiple stacks of data. This is the code I have so far, but it overwrites the existing saved file when I try to record multiple stacks. How do I get this code to save each acquired source data stack into a matrix?

N = 5; % number of stacks

timeBtw = 4; % time between stacks

timeBuff = 3; % buffer time

buffer = zeros(timeBuff/dt,1);

trigger = 1.5*[s_square;s_buffer];

source = 0.5*[s;s_buffer];

for i=1:N

[data,startTime] = readwrite(ad2,[source trigger]);

pause(timeBtw)

end