F28027 GPIO16 GPIO17一直高电平

您好，以下是我设置F28027gpio初始化程序，但是GPIO16，17一直高电平，但是GPIO4就可以设置为低电平，不知道怎么回事呢？

EALLOW;
GpioCtrlRegs.GPAQSEL1.all = 0x0000; // GPIO0-GPIO15 Synch to SYSCLKOUT
GpioCtrlRegs.GPAMUX1.all = 0x0000; // GPIO functionality GPIO16-GPIO31


GpioCtrlRegs.GPAMUX2.all = 0x0000; // GPIO functionality GPIO16-GPIO31
GpioCtrlRegs.GPADIR.all = 0xFFFF; // GPIO0-GPIO31 are GP OUTputs
GpioCtrlRegs.GPAQSEL2.all = 0x0000; // GPIO16-GPIO31 Synch to SYSCLKOUT
GpioDataRegs.GPADAT.all = 0xFFFFFFFF; //GPIO0-GPIO31 initial value are 0

GpioCtrlRegs.GPBMUX1.all = 0x0000; // GPIO functionality GPIO32-GPIO34
GpioCtrlRegs.GPBDIR.all = 0xFFFF; // GPIO32-GPIO34 are OUTputs
GpioCtrlRegs.GPBQSEL1.all = 0x0000; // GPIO32-GPIO34 Synch to SYSCLKOUT
GpioDataRegs.GPBDAT.all = 0xFFFFFFFF; //GPIO0-GPIO31 initial value are 0

GpioCtrlRegs.GPAPUD.all = 0xFFFF; // Pullup's disabled GPIO0-GPIO31
GpioCtrlRegs.GPBPUD.all = 0xFFFF; // Pullup's disabled GPIO32-GPIO34

GpioDataRegs.GPACLEAR.bit.GPIO4 = 1;
GpioDataRegs.GPACLEAR.bit.GPIO16 = 1;
GpioDataRegs.GPACLEAR.bit.GPIO17 = 1;

EDIS;