F28335有三种32位的I/O口，依次PORTA(GPIO0-GPIO31)， PORTB(GPIO32-GPIO63), PORTC(GPIO64-GPIO87)，这些口都可以配置为普通的数字IO口同样也能被配置为外部接口。这样涉及到了IO的寄存器，IO口共有三类寄存器：控制寄存器、数据寄存器和中断控制寄存器。下面依次介绍这些寄存器。
struct GPIO_CTRL_REGS {
union GPACTRL_REG GPACTRL; // GPIO A Control Register (GPIO0 to 31)
union GPA1_REG GPAQSEL1; // GPIO A Qualifier Select 1 Register (GPIO0 to 15)
union GPA2_REG GPAQSEL2; // GPIO A Qualifier Select 2 Register (GPIO16 to 31)
union GPA1_REG GPAMUX1; // GPIO A Mux 1 Register (GPIO0 to 15)
union GPA2_REG GPAMUX2; // GPIO A Mux 2 Register (GPIO16 to 31)
union GPADAT_REG GPADIR; // GPIO A Direction Register (GPIO0 to 31)
union GPADAT_REG GPAPUD; // GPIO A Pull Up Disable Register (GPIO0 to 31)
Uint32 rsvd1;
union GPBCTRL_REG GPBCTRL; // GPIO B Control Register (GPIO32 to 63)
union GPB1_REG GPBQSEL1; // GPIO B Qualifier Select 1 Register (GPIO32 to 47)
union GPB2_REG GPBQSEL2; // GPIO B Qualifier Select 2 Register (GPIO48 to 63)
union GPB1_REG GPBMUX1; // GPIO B Mux 1 Register (GPIO32 to 47)
union GPB2_REG GPBMUX2; // GPIO B Mux 2 Register (GPIO48 to 63)
union GPBDAT_REG GPBDIR; // GPIO B Direction Register (GPIO32 to 63)
union GPBDAT_REG GPBPUD; // GPIO B Pull Up Disable Register (GPIO32 to 63)
Uint16 rsvd2[8];
union GPC1_REG GPCMUX1; // GPIO C Mux 1 Register (GPIO64 to 79)
union GPC2_REG GPCMUX2; // GPIO C Mux 2 Register (GPIO80 to 95)
union GPCDAT_REG GPCDIR; // GPIO C Direction Register (GPIO64 to 95)
union GPCDAT_REG GPCPUD; // GPIO C Pull Up Disable（上拉禁止） Register (GPIO64 to 95)
};
其中GPXCTRL寄存器的作用是设置采样窗周期T=2*GPXCTRL*Tsysclk；GPxQSEL中每两位控制一个引脚，确定是3周期采样还是6周期采样或者不用采样；GPxMUX的功能很简单就是配置各个引脚的功能，或者是数字IO口，或者是外部接口。同样是两位控制一个引脚；GPxDIR是控制每个引脚的输入或是输出，0是输入，1是输出。还有一个GPxPUD寄存器，是用来使能或禁止指定接口的内部上拉。以上这些就是属于IO口的控制寄存器。下面的是IO数据类寄存器所有集合
struct GPIO_DATA_REGS {
union GPADAT_REG GPADAT; // GPIO Data Register (GPIO0 to 31)
union GPADAT_REG GPASET; // GPIO Data Set Register (GPIO0 to 31)
union GPADAT_REG GPACLEAR; // GPIO Data Clear Register (GPIO0 to 31)
union GPADAT_REG GPATOGGLE; // GPIO Data Toggle Register (GPIO0 to 31)
union GPBDAT_REG GPBDAT; // GPIO Data Register (GPIO32 to 63)
union GPBDAT_REG GPBSET; // GPIO Data Set Register (GPIO32 to 63)
union GPBDAT_REG GPBCLEAR; // GPIO Data Clear Register (GPIO32 to 63)
union GPBDAT_REG GPBTOGGLE; // GPIO Data Toggle Register (GPIO32 to 63)
union GPCDAT_REG GPCDAT; // GPIO Data Register (GPIO64 to 95)
union GPCDAT_REG GPCSET; // GPIO Data Set Register (GPIO64 to 95)
union GPCDAT_REG GPCCLEAR; // GPIO Data Clear Register (GPIO64 to 95)
union GPCDAT_REG GPCTOGGLE; // GPIO Data Toggle Register (GPIO64 to 95)
Uint16 rsvd1[8];};这些寄存器就是为了写数据，读数据用的。
再下面就是中断寄存器struct GPIO_INT_REGS {
union GPIOXINT_REG GPIOXINT1SEL; // XINT1 GPIO Input Selection
union GPIOXINT_REG GPIOXINT2SEL; // XINT2 GPIO Input Selection
union GPIOXINT_REG GPIOXNMISEL; // XNMI_Xint13 GPIO Input Selection
union GPIOXINT_REG GPIOXINT3SEL; // XINT3 GPIO Input Selection
union GPIOXINT_REG GPIOXINT4SEL; // XINT4 GPIO Input Selection
union GPIOXINT_REG GPIOXINT5SEL; // XINT5 GPIO Input Selection
union GPIOXINT_REG GPIOXINT6SEL; // XINT6 GPIO Input Selection
union GPIOXINT_REG GPIOXINT7SEL; // XINT7 GPIO Input Selection
union GPADAT_REG GPIOLPMSEL; // Low power modes GP I/O input select
};
以上就是IO口的外部中断寄存器，我们可以对上面GPIO0-GPIO63进行外部中断配置。