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Forum: USB
Topic: USB HID KEYBOARD (Search a Programmer)

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Message to Edit: HTML is ON UBB Code is OFF Smilies Legend	Originally posted by Tsuneo on 08-29-2007 05:24 AM Before continuing on the implementation of class specific requests and endpoint handling, it's better to explain about the report format. <b>INPUT report</b> INPUT report is sent from the device to host PC. As the report descriptor defines, the INPUT report is formatted as follows; one byte of modifier byte and 6 bytes keycode array. <blockquote>byte 0 Modifier byte 1 reserved 2 keycode array (0) 3 keycode array (1) 4 keycode array (2) 5 keycode array (3) 6 keycode array (4) 7 keycode array (5)</blockquote> The bitmap of modifier byte is defined in the HID spec. 8.3 Report Format for Array Items (HID1_11.pdf p56) <blockquote>bit 0 LEFT CTRL 1 LEFT SHIFT 2 LEFT ALT 3 LEFT GUI 4 RIGHT CTRL 5 RIGHT SHIFT 6 RIGHT ALT 7 RIGHT GUI</blockquote> This assignment is done by this part of the report descriptor <blockquote>Usage Page (Key Codes); Usage Minimum (224), <--- LeftControl Usage Maximum (231), <--- Right GUI</blockquote> "HID Usage Tables" spec defines keycode 10 Keyboard/Keypad Page (0x07) (Hut1_12.pdf p54) Available range of keycode is also defined in the report descriptor <blockquote>Usage Page (Key Codes), Usage Minimum (0), <--- no event indicated Usage Maximum (101), <--- Application</blockquote> While no key is pushed, all report bytes are '0'. This section of the HID spec shows the transition of the report while user types keys. 8.3 Report Format for Array Items (HID1_11.pdf p56) In this example, ALT+CTRL+DEL are keyed in and released. <blockquote><pre><font size="2">Transition Modifier Byte keycode Array (0) LEFT ALT down 00000100 00 RIGHT CTRL down 00010100 00 DEL down 00010100 4C <--- DEL keycode DEL up 00010100 00 RIGHT CTRL up 00000100 00 LEFT ALT up 00000000 00</font></pre></blockquote> Please note, the report shows a 'snapshot' of the state of pushed keys. The keycode array can hold up to 6 keys which are simultaneously pushed. The order of keycode in the array is arbitrary. When more than 6 keys are pushed at the same time, ErrorRollOver (0x01) is filled to all six bytes in the array. <blockquote>Appendix C: Keyboard Implementation (HID1_11.pdf p62) The keyboard must report a phantom state indexing Usage(ErrorRollOver) in all array fields whenever the number of keys pressed exceeds the Report Count.</blockquote> <b>OUTPUT report</b> OUTPUT report is sent from host PC to the device. The report descriptor defines a byte for five LEDs on the output report. <blockquote>bit 0 CAPS LOCK 1 NUM LOCK 2 SCROLL LOCK 3 COMPOSE 4 KANA 5-7 reserved</blockquote> This assignment derives from the LED usage, defined in the "HID Usage Tables" spec 11 LED Page (0x08) (Hut1_12.pdf p62) And this definition in the report descriptor makes the assignment. Usage Page (Page# for LEDs), Usage Minimum (1), <-- CAPS LOCK Usage Maximum (5), <-- KANA To be continued ;) Tsuneo [This message has been edited by Tsuneo (edited August 29, 2007).]
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