可能是晶振的問題。板子外接10MHz晶體振盪器，TLC2543時鐘要求4MHz。這該如何實現，在程序裏延時可以麽？

#define io_clk PORTAbits.RA0
#define io_clk_dir TRISAbits.TRISA0
#define ad_data_in PORTAbits.RA1
#define ad_data_in_dir TRISAbits.TRISA1

#define ad_data_out PORTAbits.RA2
#define ad_data_out_dir TRISAbits.TRISA2
#define ad_cs PORTAbits.RA3
#define ad_cs_dir TRISAbits.TRISA3
#define ad_eoc PORTAbits.RA4
#define ad_eoc_dir TRISAbits.TRISA4

#define port_out 0
#define port_in 1

void ad_setup();
unsigned int ad_setgetchannel(unsigned char channel);

unsigned int ad_data;

void main(void)
{
ad_setup();
while(1)
{
ad_data = ad_setgetchannel(0);
Nop();
Nop();
}
}

//call this once to set it up
void ad_setup()
{

ad_data_in_dir = port_out;
ad_data_out_dir = port_in;

io_clk_dir = port_out;
ad_cs_dir = port_out;
ad_eoc = port_in;
ad_cs = 1;
}

unsigned int ad_setgetchannel(unsigned char channel)
{
signed char i;
unsigned int data = 0x0;
unsigned int ch_config;

i=0;
do
{} while( ad_eoc == 0);


io_clk = 0;
ad_cs = 0;
/
for (i=0;i<12;i++)
{
data <<=1;
data |=ad_data_out;

if (channel&=0x80) ad_data_in =1;
else ad_data_in = 0;

io_clk=1;
channel <<= 1;
io_clk=0;
}
ad_cs = 1;
return data;
}

請幫我看下有什麽問題麽？在watch窗口裏看到ad_data值總是零。我用的18f452。spi接口另有用処所以用軟件模擬了spi。