Mitsubishi DS907x SIP, DS5000TK manual REAL±TIME Clock, DS1215 Phantom Time Chip, 144

USER'S GUIDE

SECTION 17: REAL±TIME CLOCK

Many user applications require a time±of±day clock. For this reason, all Secure Microcontroller modules have real±time clock (RTC) options. These include the DS5000T DIP and the DS2250T, DS2251T, and DS2252T SIMMs. In addition, users of the monolithic microprocessor chips will frequently connect to a Dallas Semiconductor RTC. There are two types of clock used in Dallas modules. These are the DS1215 Phantom Time Chip and the generally superior DS1283 Watch- dog Timekeeper Chip.

This section is intended to provide only a brief overview of the RTCs used on the time±microcontroller modules. For a more detailed description, please consult the Dal- las Semiconductor Timekeeping & NV RAM Data Book.

DS1215 PHANTOM TIME CHIP

The DS5000T and DS2250T microcontrollers use a custom device similar to the DS1215 Phantom Time Chip. This clock gives permanently powered time±of± day monitoring. The clock runs from an internal 32 KHz crystal and is generally independent of the microcontrol- ler. It provides time of day information including 0.01 second, seconds, minutes, hours, day, date, month and year. The register format is shown below. The DS1215 keeps time to two minutes per month accuracy. It offers a complete representation of time and calendar in a con- venient BCD format. It does not provide any interrupt

capability. These functions are provided in the DS1283 type clock that is used in the DS2251T and DS2252T.

The RTC used in the DS5000T/DS2250T is transparent to the memory map. Figure 17±1 shows a functional block diagram of the interconnection between the DS5000FP and RTC used on the DS5000T/DS2250T. It is fundamentally a serial device that resides on the address bus. To access the clock, the user must set the ECE2 bit at MCON.2 to a logic 1. This will cause all

MOVX instructions to access CE2 instead of CE1. Once ECE2 is set, the Byte±wide Address bit 2 serves as a write enable and Address bit 0 serves as the data input. Bit 7 of the Byte±wide Data bus serves as the data output. Notice that the read/write line is not used.

For each CE2 access, the DS1215 will watch the value of A0 on the Byte±wide bus for a particular 64±bit secu- rity pattern. This pattern checking prevents accidentally invoking the clock. Since these must be write opera- tions, A2 must be a logic 0 for each write. The clock will take no action unless the 64 pattern bits are written in the correct order. Any error causes the pattern comparator to start over. Thus the users must ªreallyº intend to communicate with the DS1215. Once the security pattern is written, the next 64 bits are time of day and calendar functions. Thus 128 read/writes are required for any time of day access. Data is written using BA0 and read using BD7. Thus the address actu- ally writes data, but data is read normally using one bit.

DS5000T/DS2250T FUNCTIONAL BLOCK DIAGRAM Figure 17±1

DS5000T OR DS2250T

CE2CE1

DS5000

CPU BA2WE

BA0D

RTC

BD7Q

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