General Description
The DP8570A is intended for use in microprocessor based
systems where information is required for multi-tasking, data
logging or general time of day/date information. This device
is implemented in low voltage silicon gate microCMOS technology
to provide low standby power in battery back-up environments.
The circuit's architecture is such that it looks
like a contiguous block of memory or I/O ports. The address
space is organized as 2 software selectable pages of 32
bytes. This includes the Control Registers, the Clock Counters,
the Alarm Compare RAM, the Timers and their data
RAM, and the Time Save RAM. Any of the RAM locations
that are not being used for their intended purpose may be
used as general purpose CMOS RAM.
Time and date are maintained from 1/100 of a second to
year and leap year in a BCD format, 12 or 24 hour modes.
Day of week, day of month and day of year counters are
provided. Time is controlled by an on-chip crystal oscillator
requiring only the addition of the crystal and two capacitors.
The choice of crystal frequency is program selectable.
Two independent multifunction 10 MHz 16-bit timers are
provided. These timers operate in four modes. Each has its
own prescaler and can select any of 8 possible clock inputs.
Thus, by programming the input clocks and the timer counter
values a very wide range of timing durations can be
achieved. The range is from about 400 ns (4.915 MHz oscillator)
to 65,535 seconds (18 hrs., 12 min.).
Power failure logic and control functions have been integrated
on chip. This logic is used by the TCP to issue a power fail
interrupt, and lock out the mp interface. The time power fails
may be logged into RAM automatically when VBB l VCC.
Additionally, two supply pins are provided. When VBB l
VCC, internal circuitry will automatically switch from the main
supply to the battery supply. Status bits are provided to indicate
initial application of battery power, system power, and
low battery detect. (Continued)

Features
Full function real time clock/calendar
Ð 12/24 hour mode timekeeping
Ð Day of week and day of years counters
Ð Four selectable oscillator frequencies
Ð Parallel Resonant Oscillator
Two 16-bit timers
Ð 10 MHz external clock frequency
Ð Programmable multi-function output
Ð Flexible re-trigger facilities
Power fail features
Ð Internal power supply switch to external battery
Ð Power Supply Bus glitch protection
Ð Automatic log of time into RAM at power failure
On-chip interrupt structure
Ð Periodic, alarm, timer and power fail interrupts
Up to 44 bytes of CMOS RAM
INTR/MFO/T1 pins programmable High/Low and pushpull
or open drain