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现象:
一端用了DS90C383B把RGB信号转换成LVDS,另一端用DS90C384接受转换为TTL信号连接到AT070TN92上。时钟设置的是25M,结果是屏亮了,但是系统在读写NANDFLASH或者进行网络操作时屏幕会闪烁。这个可能是什么原因?谢谢!
解决办法:
摘自CSDN的论坛 仅作记录 需要时查看
(1)时钟和数据是同步输出的;
(2)如果AHB总线冲突,会优先保证内存的传输,LCD数据会延迟传输,这样会使时钟输出不稳定,我在测试的时候时钟的确有这样的情况;
(3)LVDS芯片都是以VCLK来作为基准时钟的,时钟不稳定会导致LVDS传输问题
这次换了Thine的LVDS芯片,居然不闪了。马上去做EMC。跟TI,三星的技术支持都;联系了很多次,问题基本上搞清楚了。
(1)根本问题是三星2440本身的问题,内部总线带宽不够,导致LCD时钟不稳定。
(2)LVDS芯片的问题,国办的芯片对时钟的要求可能更高,而且Thine的芯片有去抖动等一些功能。据TI的技术支持讲这个问题已经反馈到TI的芯片设计团队,不知道以后会不会有改进。
(3)PCB布板。我在布板时主要关注的是等长,根据TI的回复,应该是差分和防止串扰更重要。
下面是技术支持的回复:
1) Receiver Skew Margin (RSKM) – The customer is most likely exceeding the RSKM limit, which is resulting in bit errors. It is important to minimize the skew between differential pairs. It is possible that at this frequency and room temperature Thine may have more margin. The National parts are typically tuned for high frequency operation.
2) Undershoot/Overshoot on the LVCMOS inputs to the C363 –I need the customer to observe the LVCMOS input voltage levels. It is important that the signals do not exceed the datasheet limits, because that will cause the ESD protection circuits to activate.
3) Layout – The picture Ted forwarded of the layout shows that the traces are not routed as 100 ohm differential impedance and in some case traces could be mutually coupled to an adjacent differential pair (2+ equally coupled to 2- and 3-).
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