关于数字电位器MCP4022T-103（U/D接口的使用）

请问谁用过数字电位器MCP4022T-103的？里面的U/D接口咋用？我用单片机模拟，似乎不行，以下是我的单片机代码，求指导。

while(1)
{

Control_Res_CS_Write(1);
CyDelay(20);
Control_Res_CS_Write(0);
CyDelay(20);

Control_Res_DA_Write(0);
CyDelay(20);
Control_Res_DA_Write(1);
CyDelay(20);
Control_Res_DA_Write(0);
CyDelay(20);
Control_Res_DA_Write(1);
CyDelay(20);
Control_Res_DA_Write(0);
CyDelay(20);
Control_Res_DA_Write(1);
CyDelay(20);
Control_Res_DA_Write(0);
CyDelay(20);
Control_Res_DA_Write(1);
CyDelay(20);

Control_Res_CS_Write(1);
CyDelay(200);
Control_Res_DA_Write(1);
CyDelay(1000);
｝