TMS320F28034: QEP模块配置问题

我按下面代码配置了QEP模块，但是输入正交编码信号后并没有产生计数值。请问还需要配置什么寄存器。

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SysCtrlRegs.PCLKCR1.bit.EQEP1ENCLK = 1;

EALLOW;
GpioCtrlRegs.GPAPUD.bit.GPIO20 = 0;
GpioCtrlRegs.GPAMUX2.bit.GPIO20 = 1;
GpioCtrlRegs.GPADIR.bit.GPIO20 = 0;
GpioCtrlRegs.GPAPUD.bit.GPIO21 = 0;
GpioCtrlRegs.GPAMUX2.bit.GPIO21 = 1;
GpioCtrlRegs.GPADIR.bit.GPIO21 = 0;
GpioCtrlRegs.GPAQSEL2.bit.GPIO20 = 0; //与系统时钟同步 EQEP1A
GpioCtrlRegs.GPAQSEL2.bit.GPIO21 = 0; //与系统时钟同步 EQEP1B
EDIS;

EQep1Regs.QDECCTL.all = 0;
EQep1Regs.QEPCTL.all = 0x9081;
EQep1Regs.QEPCTL.all = 0x900A;
EQep1Regs.QCAPCTL.all = 0x8010;
EQep1Regs.QPOSCTL.all = 0;
EQep1Regs.QPOSINIT = 0;
EQep1Regs.QPOSMAX = 0x0FFFF;
EQep1Regs.QWDPRD = 0x0FFFF;
EQep1Regs.QEINT.all = 0x0078;

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