CDP1879,
CDP1879C-1
CMOS Real-Time Clock
March 1997
Features
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).
• 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
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.
• Power Down 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.
• Separate Clock Output Selects 1 of 15 Square Wave
Signals
• Interrupt Output Activated By Clock Output and/or
Alarm Circuit
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.
• 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
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.
- External Clock Operation at 10V or 5V. . . . 4.19MHz,
2.09MHz, 1.048MHz or 32kHz
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).
• 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
Ordering Information
TEMP
RANGE
PKG.
NO.
PACKAGE
5V
10V
o
Pinout
PDIP
-40 C to
CDP1879CE1 CDP1879E
E24.6
o
+85 C
CDP1879, CDP1879C-1 (PDIP, SBDIP)
o
SBDIP
Burn-In
-40 C to
CDP1879CD1
-
-
D24.6
D24.6
TOP VIEW
o
+85 C
CDP1879CD1X
INT
RESET
POWER DOWN
RD
1
2
3
4
5
6
7
8
9
24
V
DD
23 XTAL
CDP1879 Modes of Operation
22 XTAL
CLK
21
OPERATION
FUNCTION
OUT
Read
1. Seconds, minutes, hours, date and month counters
2. Status register to identify interrupt source
IO/MEM
TPB/WR
TPA
20 DB7
19 DB6
18 DB5
17 DB4
16 DB3
15 DB2
14 DB1
13 DB0
Write
1. Control register to set device operation
2. Seconds, minutes, hours, date and month counters
3. Alarm latches for alarm time
CS
A2
Power Down
Interrupt
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”
A1 10
A0 11
1. Clock out as source
V
12
SS
2. Alarm time as source
3. Either interrupt can occur during normal or power
down mode
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
File Number 1360.2
http://www.intersil.com or 407-727-9207 | Copyright © Intersil Corporation 19949-104
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