USER'S GUIDE

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).

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Mitsubishi DS907x SIP, DS5000TK manual DS1283 RTC Interrupts, Alarm Maskbit Operation ±9, Days, Alarm Condition