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USB连接无法识别

把USB虚拟串口的官方例程烧进TM4C123的开发板里没有问题 但是烧进我自己做的板子里就无法识别

自己做的板子供电和晶振工作都正常 引脚连接也正确 SWD也能识别 但插上USB就是无法识别

硬件连接就是PD4接DM PD5接DP吧 我给DP加1.5K上拉电阻也没用

microUSB的接头封装也肯定是对的 以前用CH340做TTL转USB也没有问题

想请教一下工程师们可能出现什么情况

  • //*****************************************************************************
    //
    // Note:
    //
    // This example is intended to run on Tiva C Series evaluation kit hardware
    // where the UARTs are wired solely for TX and RX, and do not have GPIOs
    // connected to act as handshake signals.  As a result, this example mimics
    // the case where communication is always possible.  It reports DSR, DCD
    // and CTS as high to ensure that the USB host recognizes that data can be
    // sent and merely ignores the host's requested DTR and RTS states.  "TODO"
    // comments in the code indicate where code would be required to add support
    // for real handshakes.
    //
    //*****************************************************************************

    这个示例就是写给官方开发板的,UART仅为TX和RX连接,没有GPIO连接以充当握手信号。

    "TODO"
    // comments in the code indicate where code would be required to add support
    // for real handshakes.
  • 你烧的是哪个历程呢?
  • 官方的usb_dev_serial
  • 我是用USB做虚拟串口 连线都跟开发板一样 开发板例程也没有GPIO握手信号