Cartridge code (200 chars):

p=pget
cls(0)n=126m=127
rule="1101110"
pset(126,126,1)
::c::
for i=1,n do
c=p(i+1,n)
c+=p(i,n)*2
c+=p(i-1,n)*4
c=7-c
d=0
if(sub(rule,c,c)=="1")d=1
pset(i,m,d)
end
memcpy(24512,24576,8192)flip()
goto c