ACT apricot - Clockoperation

KEYBOARD
CLOCK OPERATION
The clock Ie, an OKI MSM 5832, has 13 internal registers
containing
the time (including seconds), the day of the
week, the date, the month and the year. The data is stored in
4 bit BCD nibbles. The IC can accommodate leap years if
appropriately
programmed and can work in 12 hour or 24
hour mode although only 24 hour mode is used by the
Apricot. The clock frequency can be adjusted by means of a
variable capacitor
on the Keyboard PCB.
The clock IC continues to keep time when the system is
not powered. This is because the IC then draws its power
from the PP3 battery contained in the compartment on the
underside of the Keyboard case (see Figure 3).
This software provides three basic functions, passing the
time and date to the System Unit, displaying the time and
date on the LCD and programming the clock with data
supplied by
the System Unit.
The System Unit requests the time by sending the
appropriate command to the Keyboard. The Keyboard
responds by
sending the time prefix character followed by
thirteen data bytes, the lower nibble contains the BCD data
and
the high nibble is all ones. The order of the data is: year,
month, date, day of the week, hours, minutes, seconds, with
tens first and units seconds.
The date and time are displayed when the appropriate
code is
sent to the Keyboard. The format on the screen is
shown in the section on the MicroScreen. The display of the
time and date stops when the clear screen command is
received.
The time or date are programmed by sending the
appropriate prefix followed by BCD data in the same format
and order as
sent from the Keyboard. Other commands can
be interleaved
with the clock data. However if date and time
program or LED commands are nested the resultant
contents of the clock chip are unpredictable. The clock is
programmed for leap years by setting bit 2 of the most
significant date digit.