driver-keyboard_2.htm

编写自己的操作系统

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size=3><FONT face="Times New Roman TUR">结论是：在键盘被打开的情况下，只要一个键发生了Press 
key的动作，就一定会产生一个Make code；只要一个键(除了"Pause/Break"键)发生了Rlease key的动作，就一定会产生一个Break 
code；无论它们在什么时候发生。而对于Repeat 
Code，则有两个条件，一是，到当前的时刻为止，最后被按下的键；二是，这个最后被按下的键，在被松开之前被按的时间超过键盘所设置的Repeat 
code“产生延迟</FONT>”。</FONT></SPAN></SPAN></SPAN></FONT></SPAN></SPAN></P>
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size=3><FONT face="Times New Roman TUR">在键盘系统中，由两根线，Data line和Clock 
line，用来控制对Scan code的检索和传递。如果Data line和Clock line都处于高电平状态，则每次8048每次检索到一个Scan 
code，就会立即将其发送给8042芯片。如果Data line为高电平，而Clock line为低电平，则每次8048每次检索到一个Scan 
code，不会立即将其发送给8042芯片，而是先将其存放在键盘的内部缓冲中，等Clock line变成高电平后，再将缓冲中的Scan 
code发送给8042。如果Data line为低电平，则8048停止对Scan code的检索，转而等待接收来自于8042的命令，这种情况下，如果Clock 
line为高电平，8048则会将接到的命令的回复数据发送给8042，否则，则无法回复这些命令。所以在8042需要向8048发送命令时，必须保证Clock 
line为高电平状态</FONT>。</FONT></SPAN></SPAN></SPAN></FONT></SPAN></SPAN></P>
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face="Times New Roman TUR">如果8042芯片收到一个来自于8048芯片的Scan 
code或者命令回复字节，经过处理后（可能存在的解码操作），会将其放入8042的Output buffer中，8042芯片会首先将状态寄存器（Status 
Register）的OBF(Output Buffer Full)标志设置，随后将Output 
port的IBF(bit-4)设为1，表示将产生一个IRQ1，然后将Clock 
line置为低电平，以禁止8042进一步接收8048的数据；然后发送一个IRQ1给Intel 
8059A可编程中断控制器，由它将中断提交给CPU，CPU收到此IRQ后，将调用此IRQ对应的ISR(中断服务程序,这就是我们键盘Driver的一个重要部分)</FONT></SPAN></SPAN></SPAN></SPAN></SPAN><SPAN 
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face="Times New Roman TUR">。随后此ISR可以从8042的数据端口60H中将Output 
buffer数据读取出来，并进行进一步的处理。当Output buffer中的数据被读取出来之后，8042会将状态寄存器的OBF标志清0，然后将Clock 
line置为高电平，以允许进一步接收8048发送来的数据</FONT>。</SPAN></SPAN></SPAN></SPAN></SPAN></FONT></FONT></P><SPAN 
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lang=EN-US><STRONG><FONT face="Times New Roman TUR" size=5>4.2.5&nbsp; Scan Code 
Set&nbsp;</FONT></STRONG></SPAN></SPAN></P>
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size=3><FONT face="Times New Roman TUR">迄今为止，IBM PC键盘共有3套Scan Code Set，最早的IBM 
PC/XT使用Scan Code Set 1，在随后的系统中，默认的都是Scan Code Set 2，后来出现了Scan Code Set 
3，但并非所有的键盘都支持。为了保证正确性，我们应该以Scan Code Set 
2为开发对象</FONT>。</FONT></SPAN></SPAN></SPAN></SPAN></SPAN></P>
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size=3><FONT face="Times New Roman TUR">Scan Code Set 1和Scan Code Set 
2是不相同的，但你可以让8042芯片帮你将从8048芯片得到的属于Scan Code Set 2的Scan Code转换为Scan Code Set 
1中对应的Scan Code，这样，你的驱动程序只需要都以一种方式——Scan Code set 1处理就行了。设置Scan Code 转换的方法为将8042 
Command Byte的bit-6清0。如果你设置了Scan Code转换，则8042在得到一个来自于8048的Scan 
Code之后，会首先将其转换为Scan Code set 1中对应的Scan Code，然后再将其放入8042的Output 
buffer中。这样Keyboard Driver从中读出的时候，就已经是属于Scan Code Set 1的Scan 
Code了</FONT>。</FONT></SPAN></SPAN></SPAN></SPAN></SPAN></P>
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lang=EN-US><SPAN 
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face="Times New Roman TUR">需要注意的是，Scan Code和ASCII码完全不相同，所以Keyboard 
Driver的一个重要任务是将Scan Code和ASCII之间建立一种映射关系，将从8042读到的Scan 
Code转换为ASCII码。这就提供了一个特性：你可以通过建立不同的映射表，将键映射成你所喜欢的方式。比如你完全可以将键“A”映射为字母“</FONT></SPAN></SPAN></SPAN></SPAN></SPAN><SPAN 
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lang=EN-US><SPAN 
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face="Times New Roman TUR">B”的ASCII码。事实上，你也可以其映射到扩展ASCII码上，以实现其它语言的输入，比如简体中文——假如你的键盘驱动中实现了GB2312的映射，则你敲击两次键盘则可以输入一个汉字</FONT>。</SPAN></SPAN></SPAN></SPAN></SPAN></FONT></P>
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