对于 Leonardo 来说,最大的特点就是可以直接模拟USB键盘鼠标。
一般来说,当我们需要发送某一个按键的时候可以直接使用Keyboard.print(‘a’)这样的方式,或者在Keyboard.h 中找到定义好的键值,比如:#define KEY_F1 0xC2。
我最近遇到一个问题:这个文件中定义的键值我无法在其他资料上找到,让人非常恼火,例如:没有一份资料上说 CAPS LOCK值为0xC1,但是使用Keyboard.h中定义的 #define KEY_CAPS_LOCK 0xC1 确实是好用的。最后才想起来应该去看一下对应的代码(开源的优点)。最终,找到的代码如下:
size_t Keyboard_::press(uint8_t k) { uint8_t i; if (k >= 136) { // it's a non-printing key (not a modifier) k = k - 136; } else if (k >= 128) { // it's a modifier key _keyReport.modifiers |= (1<<(k-128)); k = 0; } else { // it's a printing key k = pgm_read_byte(_asciimap + k); if (!k) { setWriteError(); return 0; } if (k & 0x80) { // it's a capital letter or other character reached with shift _keyReport.modifiers |= 0x02; // the left shift modifier k &= 0x7F; } } // Add k to the key report only if it's not already present // and if there is an empty slot. if (_keyReport.keys[0] != k && _keyReport.keys[1] != k && _keyReport.keys[2] != k && _keyReport.keys[3] != k && _keyReport.keys[4] != k && _keyReport.keys[5] != k) { for (i=0; i<6; i++) { if (_keyReport.keys[i] == 0x00) { _keyReport.keys[i] = k; break; } } if (i == 6) { setWriteError(); return 0; } } sendReport(&_keyReport); return 1; }
就是说,当我们使用KEY_CAPS_LOCK ==0xC1,会先有一个 193-136=57的动作,最后发送出去的实际上是 57(0x39),在USB HID Usage Tables 有下面的定义:
同样的文档中我们可以查到 Scroll Lock == 71(0x47) Num Lock == 83 (0x53)。于是,定义如下:
#define KEY_SCROLL_LOCK 0xCF
#define KEY_NUM_LOCK 0xDB
最终,我们编写一个代码,能让键盘上的三个LED逐次亮灭
#include "Keyboard.h" #define KEY_SCROLL_LOCK 0xCF #define KEY_NUM_LOCK 0xDB void setup() { pinMode(A0, INPUT_PULLUP); Keyboard.begin(); while (digitalRead(A0) == HIGH) { // do nothing until pin 2 goes low delay(500); } } void loop() { Keyboard.write(KEY_NUM_LOCK); Keyboard.releaseAll(); delay(1000); Keyboard.write(KEY_NUM_LOCK); Keyboard.releaseAll(); delay(1000); Keyboard.write(KEY_CAPS_LOCK); Keyboard.releaseAll(); delay(1000); Keyboard.write(KEY_CAPS_LOCK); Keyboard.releaseAll(); delay(1000); Keyboard.write(KEY_SCROLL_LOCK); Keyboard.releaseAll(); delay(1000); Keyboard.write(KEY_SCROLL_LOCK); Keyboard.releaseAll(); delay(1000); }