单片机,数码管显示cs1,cs2,wr

cs1=P0^0;
cs2=P0^1;
wr=P0^2;
void smgxs( unsigned char m, n)
{
P0 = seg7[m];
wr = 0;
cs1 = 0;
wr = 1;
cs1 = 1;
wr = 0;
P0 = smgw[n];
wr = 0;
cs2 = 0;
wr = 1;
cs2 = 1;
P0 = 0xff;//为什么加了下面这写数码管不显示乱玛?
wr = 0;
cs2 = 0;
wr = 1;
cs2 = 1;
}
都是怎么工作的 cs1,cs2,wr有什么做用,
为什么我把wr的位子该动就不行了,那位能帮小弟我一下,谢了