+Address, Handler ID and bits(Register3)
+ 1514131211 . . 8 7 . . . . . . 0
+ | | | | | | | | | | | | | | | |
+ | | | | | | | | +-+-+-+-+-+-+-+- Handler ID
+ | | | | +-+-+-+----------------- Address
+ | | | +------------------------- 0
+ | | +--------------------------- Service request enable(1 = enabled)
+ | +----------------------------- Exceptional event(alwyas 1 if not used)
+ +------------------------------- 0
+
+ADB Bit Cells
+ bit cell time: 70-130us
+ low part of bit0: 60-70% of bit cell
+ low part of bit1: 30-40% of bit cell
+
+ bit cell time 70us 130us
+ --------------------------------------------
+ low part of bit0 42-49 78-91
+ high part of bit0 21-28 39-52
+ low part of bit1 21-28 39-52
+ high part of bit1 42-49 78-91
+
+
+ bit0:
+ 70us bit cell:
+ ____________~~~~~~
+ 42-49 21-28
+
+ 130us bit cell:
+ ____________~~~~~~
+ 78-91 39-52
+
+ bit1:
+ 70us bit cell:
+ ______~~~~~~~~~~~~
+ 21-28 42-49
+
+ 130us bit cell:
+ ______~~~~~~~~~~~~
+ 39-52 78-91
+
+ [from Apple IIgs Hardware Reference Second Edition]
+
+Keyboard Handle ID
+ Apple Standard Keyboard M0116: 0x01
+ Apple Extended Keyboard M0115: 0x02
+ Apple Extended Keyboard II M3501: 0x02
+ Apple Adjustable Keybaord: 0x10
+
+ http://lxr.free-electrons.com/source/drivers/macintosh/adbhid.c?v=4.4#L802
+