Commodore Amiga A2000 - Reset Warning; Hard Reset

RESET WARNING
NOTE
Available on some A1000 and A2000 keyboards. You cannot rely on this feature for all
Amiga’s.
The keyboard has the additional task of resetting the computer on the command of the
user. The user initiates Reset Warning by simultaneously pressing the CTRL key and the
two "AMIGA" keys.
The keyboard responds to this input by syncing up any pending transmit operations. The
keyboard then sends a "reset warning" to the Amiga. This action alerts the Amiga
software to finish up any pending operations (such as disk DMA) and prepare for reset.
A specific sequence of operations ensure that the Amiga is in a state where it can respond
to the reset warning. The keyboard sends two actual "reset warning" keycodes. The Amiga
must handshake to the first code like any normal keystroke, else the keyboard goes
directly to Hard Reset. On the second "reset warning" code the Amiga must drive KDAT
low within 250 milliseconds, else the keyboard goes directly to Hard Reset. If the all the
tests are passed, the Amiga has 10 full seconds to do emergency processing. When the
Amiga pulls KDAT high again, the keyboard finally asserts hard reset.
If the Amiga fails to pull KDAT high within 10 seconds, Hard Reset is asserted anyway.
HARD RESET
NOTE
This happens after Reset Warning. Valid for all keyboards except the Amiga 500.
The keyboard Hard Resets the Amiga by pulling KCLK low and starting a 500 millisecond
timer. When one or more of the keys is released AND 500 milliseconds have passed, the
keyboard will release KCLK. 500 milliseconds is the minimum time KCLK must be held low.
The maximum KCLK time depends on how long the user holds the three keys down.
NOTE
Circuitry on the Amiga motherboard detects the 500 millisecond KCLK pulse.
- 348 Appendix H -