使用S12X的EBI，读数据正常，写数据写不进去，不知道为什么原因，请高手指教

程序如下：

#define EXT_SEG00 (*((INT8U *)0x008000))

void main(void) {

DisableInterrupts;
CRG_init(); //系统时钟初始化40M
SCIInit(9600); //串口初始化，波特率为9600

EBICTL0=0x06; //0b00010110
// ||||||
//扩展模式设置 // || | -
// ||-------10110:ASIZ[4:0]:ADDR[21-1]
// |---------0,DATA[15:8] UDS and LDS disabled ,只用到低8位
//2.Enable appropriate chip select signal (CS3E:CS0E)through the MMCCTRLO register
//MMC control register
MMCCTL0 = 0x08; //Enable CS3 chip select 0x00_0800-0x0F_FFFF


//3.Select the desired number of stretch cycles (6 read m,2Write) and disable
//the external wait feature through the EBICTRL1 register

//4.Set MCU into normal expanded mode through the MODE Register
MODE=0xA0;//Normal expanded mode,MODC = 1, MODB = 0, MODA = 1 (Normal Expanded Mode)

EXT_SEG00=0xAA; //写入数据
delayms(1000); //写入后延时



// SCISend1(temp); // 读出数据为0xFF;
SCISend1(EXT_SEG00);

SCISend1((INT8U)(*((INT8U *)0x008001)));
SCISend1((INT8U)(*((INT8U *)0x008002)));

}

读出来数据仍是没有写入数据之前的数据FF FF FF 为什么数据写不进去呢？