用stm32开发板的串口2与另一个器件通信，都是TTL电平，串口2的PA2和PA3的输入输出模式应该如何设置？

void COM2_Init(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
USART_InitTypeDef USART_InitStructure;

USART_InitStructure.USART_BaudRate = 4800; //波特率
USART_InitStructure.USART_WordLength = USART_WordLength_8b; //数据位
USART_InitStructure.USART_StopBits = USART_StopBits_1; //停止位
USART_InitStructure.USART_Parity = USART_Parity_No; //奇偶校验
USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None; //数据流控制
USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx; //模式
/* 开启GPIO时钟 */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2, ENABLE);
/* Configure USART Tx as alternate function push-pull */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);

/* Configure USART Rx as input floating */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/* USART configuration */
USART_Init(USART2, &USART_InitStructure);

/* Enable USART1 Receive interrupts */
USART_ITConfig(USART2, USART_IT_RXNE, ENABLE);

/* Enable USART */
USART_Cmd(USART2, ENABLE);
}