Apple Lisa - Page 37

Confidential
Lisa Hardware Reference Manual
SETTING THE CLOCK
The s bit, if set, enables Clock Set mode, and the 16 nibbles of
time data can be entered one digit (nibble) at a time. Only as
many nibbles as desired need to be entered during the time setting
operation. Once the time has been set, the s bit is cleared, and
the operation is terminated. The clock and timer must be stopped
while the time is being set. To do this, set the clock mode to
Clock/Timer disable ($00) during the operation, then reset it to
Timer disable ($01) when the operation is complete. The clock
can be left running while setting the alarm, but the timer must be
disabled ($01).
The order in which the time information is entered during the time
set operation is:
aaaaa y ddd hh mm sa t
where:
aaaaa
alarm nibbles
(O-$FFFFF)
y
year (0-15)
ddd day (1-366)
hh hour (0-23)
mm minute (0-59)
ss second (0-59)
t
tenth of second
(O~)
7-Jul-81
The alarm counts down one count per second and generates an interrupt
upon the $00000 -> $FFFFF transition. Since the five alarm nibbles are
entered first, the alarm can be set without disturbing the clock.
All the nibbles are maintained in decimal format except the alarm
and year nibbles which are kept in binary format to reduce the
amount of code required to handle them.
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