各位好，小弟目前在自修"An Embedded Software Primer"。其中里面有一些看不懂的疑 问 图片:http://imgur.com/a/97LLF http://imgur.com/a/9cuOz http://imgur.com/a/xWo9r 在第一张图片中，the open collector outputs, allows you to attach the outputs of several devices together to drive a single signal. Unlike the usual outputs, which drive signals high or drive them low, the open collector outputs can drive their outputs low or let them float. 想请问一下这一段。open collector outputs可以让Chip 1跟Chip 2的outputs为low 或 float。是因为在Chip1跟Chip2的输出有一个inverter吗? 什麽是usual outputs?是指输出 没接其他的外部电路吗? 在第二张图片中，If several open collector outputs are attached to the same signal, then the signal goes low if any of the outputs is driving low. open collector outputs不是只有一个吗?为什麽会有好几个? 这里的same signal是指哪 个signal? pullup resistor上的signal吗? 同样在第二张图片中，为什麽一定要有pullup resistor?为什麽没有的话，INT/会float? pullup resistor是接到VCC，就算没有这颗电阻，INT/也是high吧? 其中，Note also that you cannot omit the resistor and connect the INT/ signal directly to VCC. If you did this, then you would have a bus fight on your hands as soon as one of the devices tried to drive INT/ low, since the parts that provide electrical power to your circuit would then try to keep INT/ high. 这句的意思是说，如果Chip 1或Chip 2想要给INT/ low，但VCC同时给high会导致bus fight，但是，为什麽加上pullup resistor就不会发生呢? 谢谢前辈们看完这冗长又基本的问题，谢谢。 --

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