Apple Lisa - Clock;Calendar Circuit

Confidential
Lisa Hardware Reference Manual
THE CLOCK/CALENDAR CIRCUIT
The clock/calendar is a part of the keyboard encoder circuitry. The
clock resolves to tenths of a second, and needs to be reset only once
every sixteen years. In addition, there is an alarm clock that can be
programmed to generate an interrupt at any time up to $FFFFF seconds
(about 12 days) from the time it is set. This interrupt, for example,
can be programmed to generate a system power up.
The 6522
Peripheral A Port data bus (PAO-PA7) is used to communicate
with the clock.
CLOCK COMMANDS
PA7-PAO Function
---------,------ ------------------
0000 0010 Read clock data
0001 nnnn Write nnnn to clock
0010 spmm Set Clock modes
CLOCK MODES
mm
00
01
10
11
Function
Clock/Timer disable
Timer disable
Timer underflow generates interrupt
Timer underflow turns system on, if it
is off, and generates an interrupt
7-Jul-81
If the p bit above is 0, the system is turned off. If the p bit is one,
and the system is off, the system is turned back on.
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