DP83848cvv 连接不稳定的原因

通过交换机    以太网udp发收包软件     有时候板子能收到数据，有时候不能收到。ping的时候有时候通，有时候不通。这么不稳定到底是什么原因。请各路大侠帮忙。项目太着急了。谢谢各位！

Jason Shen：

如果不是硬件的问题，就是软件的问题。我们的DP83848是负责物理接口的部分，如果是因为这一块信号连接不稳定，可以尝试直接连接到电脑调试，如果是系统软件的问题，建议优化

xiangjie xu：

回复 Jason Shen:

将代码下载到别人的开发板上能用运行。自己的板子 不能运行。说明不是代码的问题。

测试方法  是通过以太网抓包工具测得。

Jeff Wang1：

回复 xiangjie xu:

你的硬件配置有问题。可以参考下面链接的原理图检查一下。

http://www.ti.com/lit/df/snlr022/snlr022.pdf?keyMatch=snlr022.pdf&tisearch=Search-EN-Everything

xiangjie xu：

回复 Jeff Wang1:

附件是我板子的硬件原理图连接图。使用RMII接口似乎没什么区别。

Jeff Wang1：

回复 xiangjie xu:

使用ＲＭＩＩ接口，原理图没有发现问题。你可以按以下step 测试一下：

Power up the board and verify key voltages

1.Probe the 3.3V supply pins
2.Probe the PFBOUT and PFBIN pins

The PFBOUT pin is a regulated 1.8V supply generated inside the device from the 3.3V supply.  The device will not operate correctly if the PFBIN pins do not receive this 1.8V supply.

3.Probe the RBIAS pin 

The voltage should be ~1.2V. The RBIAS pin sets the main reference bias for the device.  If the voltage or current for this pin is not correct, it could affect the entire device. 

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Power down the board and verify key resistances

1.Resistance to ground across the RBIAS resistor should be 4.87 kOhms +/- 1%
2.Resistance across the transmit and receive terminations should be 50 Ohms +/- 1%
3.Resistance across the MDIO pull-up resistor should be approximately 1.5 kOhms

Problems can occur when a very small (10's of Ohms) pull-up resistor is used.

Power up the board and verify key signals

1.Probe the RESET_N signal

The reset input is active low and is connected to a 10 kOhm pull down resistor.  It is important to confirm that the controller is  not driving the RESET_N signal low.  Otherwise, the device will be held in reset and will not respond.

2.Probe the X1 clock

Verify the frequency and signal integrity.  For link integrity the clock needs to be within +/- 50ppm of the default (25MHz for MII / 50MHz for RMII). 

3.Probe the TD+/- transmit signals

Measure the transmit voltages using a

  100 Ohm terminated Pig-tail cable 

4.Probe strap pins during initialization. 

In some cases, other devices on the board (e.g. MAC) will pull or drive these pins unexpectedly.