Rainbow Electronics DS12887 - Manual (Page 2)

DS12887
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TYPICAL OPERATING CIRCUIT
DESCRIPTION
The DS12887 real-time clock (RTC) plus RAM is designed to be a direct replacement for the DS1287.
The DS12887 is identical in form, fit, and function to the DS1287, and has an additional 64 bytes of
general-purpose RAM. Access to this additional RAM space is determined by the logic level presented on
AD6 during the address portion of an access cycle. A lithium energy source, quartz crystal, and write-
protection circuitry are contained within a 24-pin dual in-line package. As such, the DS12887 is a
complete subsystem replacing 16 components in a typical application. The functions include a nonvolatile
time-of-day clock, an alarm, a 100-year calendar, programmable interrupt, square-wave generator, and
114 bytes of NV SRAM. The RTC is unique in that time-of-day and memory are maintained even in the
absence of power.
OPERATION
The block diagram in Figure 1 shows the pin connections with the major internal functions of the
DS12887. The following paragraphs describe the function of each pin.