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SN65lbc184差分信号不正常

Other Parts Discussed in Thread: SN65LBC184

SN65LBC184,5V供电,用电脑的串口助手通过USB转485线发送数据给SN65LBC184,示波器测量A、B线的电平,发现一上电就变成下图二所示,RX脚根本不能识别出信号,换了十个芯片都这样,也分别试了A和B上下拉1k或者20K电阻。图一是没上电前的,此时信号正常。实在搞不定,求教!

图一

图二

  • 那方便做这样一下测试吗,目的是看芯片功能是否正常,根据数据手册driver和receiver的真值表,当driver enable的时候,给D一个脉冲,Vih(min)=2V,Vil(max)=0.8V,示波器测量下AB,同样再测试下receiver的情况。