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add note about C-A-A behaviour on A1200 keyboard (nw)

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This commit is contained in:
Vas Crabb 2018-08-15 19:07:13 +10:00
parent 8e2ffd5446
commit b668d1d3ca
1 changed files with 9 additions and 0 deletions
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src/devices/bus/amiga/keyboard/a2000.cpp
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@ -43,6 +43,15 @@
ceramic resonator, a TI SN74HC00N, and a Hitachi HD74HC123AP. The
header for the host connection has four positions and pins.
When the third key of the Ctrl-Amiga-Amiga sequence is pressed, the
keyboard will pull CLOCK low for 272,007 machine cycles (680ms - a
normal CLOCK pulse is 4 machine cycles, or 10µs), followed by the
power-up code 0xFE 1,706 machine cycles (4.265ms) later. This is
repeated every 280,787 machine cycles (702ms) as long as the keys
are held. Supposedly if the host chipset detects CLOCK has been
pulled low for at least 60ms, it will generate a 250ms reset pulse
when CLOCK is released.
***************************************************************************/
#include "emu.h"