CDP1879 Intersil Corporation, CDP1879 Datasheet - Page 13

• Manufacturer Part Number: CDP1879
• Description: CMOS Real-Time Clock
• Manufacturer: Intersil Corporation

NOTE:
Applications
A typical application for this real-time clock is as a wake-up
control to a CPU to reduce total system power in intermit-
tent-use systems. A hookup diagram illustrating this feature
is shown in Figure 10. In this configuration, the alarm and
power-down features of the CDP1879 are utilized in the con-
trol of the sleep and wake-up states of the CPU. A typical
shut-down/start-up sequence for this system could proceed
as follows:
1. The CPU has finished a current task and will be inactive
2. The CPU loads the CDP1879 alarm registers with the
3. The CDP1800 Q output is set high, which stops the CPU
V
Chip Deselect to Standby
Recovery to Normal
1. t
FIGURE 8. STANDBY (TIMEKEEPING) VOLTAGE AND TIMING
CS
DD
(Timekeeping) Voltage Time
Operation Time
for the next six hours.
desired wake-up time.
oscillator (as an alternative, in an NMOS system, power
to all components except the clock chip could be shut off).
R
t
STBY
, t
F
1 s
WAVEFORMS
V
V
IH
PARAMETER
IL
0.95 V
STANDBY (TIMEKEEPING) CHARACTERISTICS AT FULL TEMPERATURE RANGE
VOLTAGE MODE
t
DD
R (NOTE 1)
STANDBY
V
STBY
t
t
CSTBY
RC
0.95 V
DD
V
V
t
IH
IL
CDP1879, CDP1879C-1
RC
t
F (NOTE 1)
V
(V)
10
10
DD
5
5
V
4-116
2.5, 3
2.5, 3
2.5, 3
2.5, 3
STBY
(V)
4. This Q output signal is received by the CDP1879 as a
5. The CDP1879 three-states the interrupt output pin.
6. The CDP1879 eventually times out, and sets an alarm by
7. The alarm signal resets the CPU (to avoid oscillator start-
8. The CPU, once into its normal software sequence, writes
FIGURE 9. TYPICAL STANDBY (TIMEKEEPING) VOLTAGE vs
power-down signal.
driving the INT output low.
up problems) and flags the processor for a warm-start
routine.
to the CDP1879 control register to reset the interrupt
request.
5
4
3
2
1
0
-40
MIN
EXTERNAL CLOCK SOURCE OF 32kHz
TYPICAL STANDBY (TIMEKEEPING) VOLTAGE
3V (-40
2.5V (-0
2
1
2
1
CDP1879
FULL TEMPERATURE RANGE
-20
o
o
C
C
FULL TEMPERATURE RANGE -
MAX
T
T +70
-
-
-
-
+85
0
LIMITS
o
o
C)
C
20
MIN
2
2
CDP1879C-1
-
-
40
MAX
60
-
-
-
-
o
C
80
UNITS
s
100