TI28335的CAN通信例程(ecan_a_to_b_xmit )问题

我在自己的板子上运行TMS32028335的CAN通信例程,名字是ecan_a_to_b_xmit ,我已将板子上的CANA和CANB连接起来,唯一改动的是CANA、B的GPIO口,但是运行程序后发现一直停在下面这个循环中(红色字体):

 for(i=0; i < TXCOUNT; i++)
   {
       ECanaShadow.CANTRS.all = 0;
       ECanaShadow.CANTRS.bit.TRS25 = 1;             // Set TRS for mailbox under test
       ECanaRegs.CANTRS.all = ECanaShadow.CANTRS.all;

       do
     {
       ECanaShadow.CANTA.all = ECanaRegs.CANTA.all;
     } while(ECanaShadow.CANTA.bit.TA25 == 0 );   // Wait for TA5 bit to be set..


       ECanaShadow.CANTA.all = 0;
       ECanaShadow.CANTA.bit.TA25 = 1;               // Clear TA5
       ECanaRegs.CANTA.all = ECanaShadow.CANTA.all;

       loopcount ++;
    }

这说明CANA一直没有收到应答信号,请问大家可以帮帮忙吗?