cdma

user1  01
spread code 0101 扩频码
XOR  01011010    异或
voltage +1 -1 +1 -1 -1 +1 -1 +1  转为电压0 => +1  1 => -1


user2  10
spread code 0011 
XOR  11000011
voltage -1 -1 +1 +1 +1 +1 -1 -1 


user3  11
spread code 0000 
XOR  11111111
voltage -1 -1 -1 -1 -1 -1 -1 -1 

========================================
add 3 way                          将3路信号相加
        -1 -3 +1 -1 -1 +1 -3 -1
        
decode user1         使用user1 扩频码（电压模式）解码
spread  +1 -1 +1 -1 +1 -1 +1 -1

multiply-1 +3 +1 +1 -1 -1 -3 +1   相加后的3路信号 和 扩频码 相乘

add chip(-1+3+1+1)=4 (-1-1-3+1)=-4  分2部分相加
divide       4/4=+1       -4/4=-1  除以4 

voltage       0            1      将电压转为原始数据