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USB主控制器问题请教
使用了一个USB主控制器,外加一个USB收发器(PDIUSBP11A),设计USB主控制器端的电路。USB收发器上有一个Mode管脚(当为低电平时,D-输出3V电压;当为高电平时,D-输出0V电压)。
首先在D+、D-上没有下拉电阻时,当插上USB全速设备时D+上电压(应该是3V)被拉低成0V; 当在D+、D-上加上15K欧姆的下拉电阻时,插上全速USB设置,D+上的电压(应该是3V)也被拉低成0V 没有下拉电阻的电路图是文档上的,不知道为什么会出现这种情况?我认为不应该被拉低啊。 |
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沙发#
发布于:2003-11-01 14:47
high speed ,usb device had one 1.5koR on D+
low speed ,usb device had one 1.5oR On D- so if plug device to Host if is hight speed device ,D+ mus to High if is low speed device ,D- must to low but as book said : on usb host D+ D- ,the pull R must 15Ko , if you usb device had no 1.5Ko R on D+orD-,I thank the D+ D- must Low alway. |
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