4-104

Features

• CPU Interface for Use with General-Purpose

Microprocessors

• Time Of Day/Calendar

• Reads Seconds, Minutes, Hours

• Reads Day of Month and Month

• Alarm Circuit With Seconds, Minutes or Hours

Operation

• Power Down Mode

• Separate Clock Output Selects 1 of 15 Square Wave

Signals

• Interrupt Output Activated By Clock Output and/or

Alarm Circuit

• Date Integrity Sampling for Clock Rollover Eliminated

• On-Board Oscillator:

- Crystal Operation CDP1879 at 10V . . . . . . . 4.19MHz,

2.09MHz or 1.048MHz

- Crystal Operation CDP1879C-1 at 5V . . . . . 4.19MHz,

2.09MHz or 1.048MHz or 32kHz

- External Clock Operation at 10V or 5V. . . . 4.19MHz,

2.09MHz, 1.048MHz or 32kHz

• Addressable in Memory Space or CDP1800 Series I/O

Mode

• Low Standby (Timekeeping) Voltage with External Clock

• Related Literature

- AN7275, Guide to the Use of CD1879 and

CDP1879C1 Real Time Clock

Pinout

CDP1879, CDP1879C-1 (PDIP, SBDIP)

TOP VIEW

Description

The CDP1879 real-time clock supplies time and calendar information

from seconds to months in BCD format. It consists of 5 separately

addressable and programmable counters that divide down an oscillator

input. The clock input can have any one of 4 possible frequencies,

allowing flexibility in the choice of crystal or external clock sources.

Using an external 32kHz clock source, timekeeping can be performed

down to 2.5V (see Standby (Timekeeping) Voltage Operation).

The device can be memory-mapped for use with any general-purpose

microprocessor and has the additional capability of operating in the

CDP1800 series input/output mode.

The real-time clock functions as a time-of-day/calendar with an alarm

capability that can be set for combinations of seconds, minutes or

hours. Alarm time is configured by loading alarm latches that activate

an interrupt output through a comparator when the counter and alarm

latch values are equal.

Fifteen selectable square-wave signals are available as a separate

clock output signal and can also activate the interrupt output. A status

register is available to indicate the interrupt source. The value in an 8 bit

control register determines the operational characteristics of the device,

by selecting the prescaler divisor and the clock output, and controls the

load and alarm functions.

A transparent “freeze” circuit preclude clock rollover during counter and

latch access times to assure stable and accurate values in the counters

and alarm latches.

The CDP1879 is functionally identical to the CDP1879C-1. The

CDP1879 has a recommended operating voltage range of 4V to 10.5V,

and the CDP1879C-1 has a recommended operating voltage range of

4V to 6.5V. The CDP1879 and the CDP1879C-1 are supplied in 24 lead

hermetic dual-in-line side-brazed ceramic packages (D suffix) and 24

lead dual-in-line plastic packages (E suffix

).

1

2

3

4

5

6

7

8

9

10

11

12

INT

RESET

POWER DOWN

RD

IO/MEM

TPB/WR

TPA

CS

A2

A1

A0

16

17

18

19

20

21

22

23

24

15

14

13

XTAL

CLK

DB7

DB6

DB4

DB2

DB1

DB0

XTAL

DB5

DB3

OUT

Ordering Information

PACKAGE

TEMP

RANGE

5V

10V

PKG.

NO.

PDIP

CDP1879CE1

CDP1879E

E24.6

SBDIP

CDP1879CD1

-

D24.6

Burn-In

CDP1879CD1X

-

D24.6

CDP1879 Modes of Operation

OPERATION

FUNCTION

Read

1. Seconds, minutes, hours, date and month counters

2. Status register to identify interrupt source

Write

1. Control register to set device operation

2. Seconds, minutes, hours, date and month counters

3. Alarm latches for alarm time

Power Down

1. Three-state interrupt output with active alarm or

clock out circuitry for wake-up control

2. Data bus and address inputs are “DON’T CARE”

Interrupt

1. Clock out as source

2. Alarm time as source

3. Either interrupt can occur during normal or power

down mode

March 1997

File Number

1360.2

CDP1879,

CDP1879C-1

CMOS Real-Time Clock

CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.

http://www.intersil.com or 407-727-9207