There is sample code in the libray look there
x1: db "0"
x2: db "1"
.
.
.
.
mov x1,"0101" ; NO

mov x1,"0"
mov x2,"1"
mov x3,"0"
mov x4,"1"

I did not Look up the mov comand. But in general
You have a source (src) and a destination (dest)
You can not move anything anywhere.
You may have to use the Accumulator
mov a,x1
mov x2,a

If you need a pointer
mov @r0
movc @dptr
movx @r0
movx @dptr

Look for the 8051 Bible in Links.