定时器8254的问题

51单片机和定时器8254，连接方法和初始化在下面。但是不能工作，求解

sbit CS=P2^6;
sbit A1=P2^4;
sbit A0=P2^3;
sbit W=P2^1;
sbit R=P2^0;
sbit GATE=P3^0;
void start_8254()
{
P2 = 0x19;
P1 = 0x36;
P2 = 0x01;
P1 = 0x20;
P2 = 0x01;
P1 = 0x20;
CS = 1;
GATE = 1;