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