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CDP1879 Schematic ( PDF Datasheet ) - GE

Teilenummer CDP1879
Beschreibung CMOS Real-Time Clock
Hersteller GE
Logo GE Logo 




Gesamt 16 Seiten
CDP1879 Datasheet, Funktion
CMOS Peripherals
CDP1879, CDP1879C-1
iN'f
RESET
POWER DOWN
iii)
X-O/MEM
TPB/Wii
TPA
CS
A2
AI
AD
VSS'
I
2
5
4
5
6
7
B
9
10
II
12
24 VDD
23 XTAL
22 XTAL
21
CLOCK
OUT
20 DB7
19 DBS
IB DBS
17 OB4
16 OB3
15 OB2
14 OBl
15 OBO
92CS-54345RI
TERMINAL ASSIGNMENT
CMOS Real-Time Clock
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
• Data integrity sampling for clock rollover eliminated
• On-board oscillator 4.19 MHz, 2.09 MHz or 1.048 MHz
@ 10 V (CDP1879) crystal operation
4.19 MHz, 2.09 MHz, 1.048 MHz or 32 kHz @ 5 V
(CDP1879C-1) crystal operation
4.19 MHz, 2.09 MHz, 1.048 MHz or 32 kHz
@ 10 V or 5 V external clock operation
• Addressable in memory space or CDP1800 series I/O mode
• Low standby (timekeeping) voltage with external clock
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 anyone of 4 possible frequencies, allowing
flexibility in the choice of crystal or external clock sources.
Using an external 32-kHz clock source, timekeeping can be
performed down to 2.5 V (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.
CDP1879 MODES OF OPERATION
OPERATION
FUNCTION
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 precludes 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-l.
The CDP1879 has a recommended operating voltage range
of 4 to 10.5 volts, and the CDP1879C-1 has a recommended
operating voltage range of 4 to 6.5 volts. The CDP1879 and
the CDP1879C-1 are supplied in 24-lead hermetic dual-in-
line side-brazed ceramic packages (0 suffix) and 24-lead
dual-in-line plastic packages (E suffix).
Read
1. Seconds, minutes, hours, date and month counters
2. Status register to identify interrupt source
Write
Power Down
Interrupt
1. Control register to set device operation
2. Seconds, minutes, hours, date and month counters
3. Alarm latches for alarm time
1. Tri-state interrupt output with active alarm or clock out circuitry for wake-up
control.
2. Data bus and address inputs are "DON'T CARE".
1. Clock out as source
2. Alarm time as source
3. Either ·interrupt can occur during normal or power down· mode
File Number 1360
452 ______________________________________________________________






CDP1879 Datasheet, Funktion
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ CMOS Peripherals
CDP1879, CDP1879C-1
GENERAL OPERATION
The real-time clock contains seconds, minutes, and hours,
date and month counters that hold time of day/calendar
information (see Fig. 2). The frequency of an intrinsic
oscillator is divided down to supply a once-a-second signal
to the counter series string. The counters are separately
addressable and can be written to or read from
The real-time clock contains seconds, minutes and hour
write-only alarm latches that store the alarm time (see Fig.
3). When the value of the alarm latches and counters are
equal, the interrupt output is activated. The Interrupt output
can also be activated by a clock output transition The clock
output is derived from the prescaler and counters and can
be one of 15 square-wave signals. The value in the read-
only interrupt status register identifies the interrupt source
Operational control of the real-time clock is determined by
the byte in a write-only control register. The 8-bit value in
this register determines the correct divisor for the prescaler,
a data direction and alarm enable bit, clock output select,
and start/stop control (see Fig. 4).
Data transfer and addressing are accomplished In two
modes of operation, memory mapping and I/O mapping
using the CDP1800-senes microprocessors. The mode is
selected by the level on an input pin. (I-O/MEM). Memory
mapping implies use of the address lines as chip selects and
address inputs using linear selection or partial or full
decoding methods. I/O mapping with the CDP1800-series
microprocessors involves use of the N line outputs In
conjunction with input and output instructions to transfer
data to and from memory.
ill
I
CLOCI< OUT
0 -V-DD
~
III
AD
AI
A2
TPA
I.-O/ME"M
TPB/WR
cs
POWER DOWN
ADDRESS OECODE
AND
CONTROL LOGIC
92CL-34913
Fig. 2 - Functional diagram - time counters highlighted.
_____________________________________________________________ 457

6 Page









CDP1879 pdf, datenblatt
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ CMOS Peripherals
CDP1879, CDP1879C-1
STANDBY (TIMEKEEPING) VOLTAGE OPERATION (Conl'd)
V DO
'~:' t~~ V~I~L~cs ______________________
*tr, If ~1"s
92CM-37UI
Fig. 8 - Standby (timekeeping) voltage- and timing-waveforms.
92CS- 31292
Fig. 9 - Typical standby (timekeeping) voltage vs. full-temperature range.
APPLICATIONS
A tYPical application forthis real-time clock is as a wake-up
control to a CPU to reduce total system power in inter-
mittent-use systems. A hookup diagram illustrating this
feature is shown in Fig. 10. In this configuration, the alarm
and power-down features of the CDP1879are utilized in the
control of the sleep and wake-up states of the CPU. A
typical shu:-down/start-up sequence for this system could
proceed as follows:
1. The CPU has finished a current task and will be inactive
for the next six hours.
2. The CPU loads the CDP1879 alarm registers with the
desired wake-up time.
3. The CDP1800 Q output is set high, which stops the
CPU oscillator (as an alternative, in an NMOS system,
power to all components except the clock chip could be
shut off).
4. This Q output signal is received by the CDP1879 as a
power-down signal.
5. The CDP1879 tri-states the interrupt output pin.
6. The CDP1879 eventually times out, and sets an alarm
by driving the TIiIT output low.
7. The alarm signal resets the CPU (to avoid oscillator
start-up problems) and flags the processor for a warm-
start routine.
8. The CPU, once into its normal software sequence,
writes to the CDP1879 control register to reset the
interrupt request.
NO I---------------~
NI A I
N2 A2
CDPl800
CDPIB79
1+---------+---_....., INT
92CS-34138R3
Fig. 10 - CPU wake-up cIrcuit using the CDP1879 real-time clock.
463

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