Mitsubishi Motors DS5000TK - Manual (Page 154)

USER’S GUIDE
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DS1283 RTC INTERRUPTS
The DS1283 provides two interrupt functions. They are
time–of–day alarm and a watchdog alarm. The watch-
dog alarm is a user programmed periodic interval time–
out. It is programmed using registers 0Ch and 0Dh. The
time–of–day alarm is controlled by the registers at loca-
tions 03h, 05h, and 07h as well as the command regis-
ter. The alarm registers relate to similar time registers.
The alarm works by matching the time to the selected
alarm according to the mask bits. These are the MSBs
of the respective alarm registers. The mask determines
if that register is used in the alarm match or is a don’t
care. There are four valid selections shown in Figure 17–9.
ALARM MASKBIT OPERATION Figure 17–9
MASK
Minutes Hours Days ALARM CONDITION
1 1 1 Alarm once per minute.
0 1 1 Alarm when minutes match time.
0 0 1 Alarm when minutes and hours match time.
0 0 0 Alarm when minutes, hours, and days match time.
Note: Other mask bit combinations produce illogical operations and should be avoided.
The DS1283 provides three interrupt outputs called
INTA, INTB, and INTP. INTP is an open–drain repre-
sentation of INTA that can also be forced active. It has
no other operational function. Either INTA and INTB
can be assigned to either interrupt function. That is,
INTA can be the time–of–day alarm or the time–out
interval alarm. When INTA serves as one function,
INTB is automatically the other. INTP always tracks with
INTA. This allows the RTC interrupts to use only one
interrupt pin on the microprocessor if the interrupts will not be used simultaneously. In the DS2251T, all three
interrupt pins are available at the connector. The user
connects these to the microprocessor port pins of
choice. In the DS2252T, only one interrupt signal is
available. It is INTP and is connected to P3.2 (INT0).
Since INTP is an open–drain signal, it will not interfere if
not used. When activated, INTP will pull P3.2 low. As
described above, the interrupt functions can be
switched so either is issued via INTP (INTA).