Mitsubishi DS907x SIP, DS5000TK manual DS1283 Watchdog Timekeeper Chip, 150

USER'S GUIDE

DS1283 WATCHDOG TIMEKEEPER CHIP

The DS2251T and DS2252T use the DS1283 Byte± wide RTC. This is also the clock of choice for users designing with the microprocessor chips (DS5000FP, DS5001FP, and DS5002FP). This clock gives perma- nently powered time±of±day monitoring. The clock runs from an internal 32 KHz crystal (in the modules) and is generally independent of the microcontroller. It pro- vides time of day information including 0.01 second, seconds, minutes, hours, day, date, month and year. The register format is shown below. The DS1283 keeps time to two minutes per month accuracy. It offers a com- plete representation of time and calendar in a conve- nient BCD format, but is accessible via the memory bus in a parallel fashion and is read or written like a RAM. It requires no security pattern or shifting to access. This is practical since the DS5001 series decodes peripheral chip enables that do not interfere with the normal memory map.

The DS1283 also offers powerful interrupt capability including a time of day/calendar alarm and a periodic interval time±out. The alarm can be set for once per

minute, when an exact minute occurs, when an exact minute and hour occurs, or when an exact minute, hour, and day occurs. This alarm generates an output that can be connected to an interrupt input on the microcon- troller. This is explained in more detail below. A second interrupt is also provided on the DS1283. It is related to a programmable interval. This interrupt will activate if the interval is allowed to time±out. It is programmable between 0.01 second and 99.99 seconds. It is also independent of the time±of±day interrupt described above. The time±out interrupt can be used as a third timer, a watchdog function or for a variety of other uses.

Figure 17±6 illustrates the DS1283 connection for the DS2251T and DS2252T. The difference between the two versions is the interrupt pin±out. A DS2251T has all of the DS1283 interrupt outputs bought to the connector. The user can determine how these are connected. The DS2252T provides one open±drain interrupt output that is connected to P3.2. Note that since it is open±drain, it will not interfere with other circuits using P3.2 if unused. These differences are discussed in more detail below.

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