Note: Descriptions are shown in the official language in which they were submitted.
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The present invention re~ates to a volatile memory hold
device which retains stored data even when the power supply
from the power source is no longer available, and more
- particularly to a volatile memory hold device wherein a
volatile memory is supplied with discharge power from a
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capacitor when the power supply from the power source is no
longer available.
- Modern electronic systems such as electronic cash
registers each comprise a logic board including an arithmetic
unit and a memory board including a plurality of volatile
memories which are C MOS RAMs (complementary metal-oxide-
semiconductor random-access-memories). Generally, the
` volatile memory, such as C MOS RAM, has the disadvantage
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that the data stored in the memory are volatilized when the
power supply thereto is cut off, e.g., by an interruption of
electric power service.~ As is well know~, a supplemental
battery is provided to obviate the disadvantage. Such a
supplemental battery is connected to the memory to prevent
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` destruction of stored data when the power from the power
source is no longer available. There still remains a
problem, however~ in that to retain the stored data, the
memory board must be maintained in electrical communication
with the supplemental battery even on dismounting of the
memory board and this requirement means a considerable
inconvenience in maintenance service.
It is, therefore, a primary object of this invention
to provide a volatile hold memory device which is simple in
construction and which prevents stored data in a volatile
memory from being volatilized even when the power supplied
thereto is no longer available.
It is another object of this invention to provide a
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volatile memory hold device which comprises a capacitor
which is charged by the power for the volatile memory and
which supplies the memory with the power discharged therefrom.
It is still another object of this invention to provide
a volatile memory hold device which holds stored data in
the memory for many hours after the power supplied to the
memory becomes unavailable.
To this end the invention consists of a volatile memory
hold device comprising power terminals to which a power
~ 10 source is connectable, a volatile memory connected to said
;~ power terminals, the latter serving as input power terminals
for said volatile memory, and a charge-and-discharge circuit
connected across said power terminals in parallel with said
memory, said charge-and-discharge circuit includïng a
capacitor and a first resistor connected in series with said
capacitor, said capacitor being charged by power for said
volatile memory supplied over said power terminals and
sUPPlyingsaid memory with power discharged therefrom, said
resistor having a resistance value which prevents application
- 20 of a rush current to said memory from said capacitor, said
charge-and-discharge circuit enabling said memory to retain
stored data even when the power supply from said power source
is no longer available.
Other features and advantages of embodiments of the
invention will become apparent from the following detailed
- description and the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a perspective view showing logic and memory
boards embodying the principles of this invention.
Fig. 2 is a schematic diagram of a v-olatile memory hold
device embodying the principles of this invention.
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Fig. 3 is a schematic diagram of another embod;ment of
the volatile memory hold device according to this invention.
Fig. 4 is a schematic diagram of another embodiment of
the volatile memory hold device according to this invention.
Fig. 5 is a schematic diagram of another embodiment of
the volatile memory hold device including a non-rechargeable
battery according to this invention.
Fig. 6 is a schematic diagram of another embodiment of
the volatile memory hold device utilizing a Zener diode
according to this invention.
Fig. 7 is a graph showing a curve of discharge voltage
of the capacitor associated with the device of Fig. 6.
DETAILED DESCRIPTION OF TIIE E~BODIMENTS
Referring, now, to Fig. 1, there is shown a logic and
a memory board embodying the principles of this invention.
An arithmetic board 1 and a memory board 2, which constitute
parts of an electronic system, are separable for maintenance
service. The memory board 2 includes volatile memories 21,
22 ...2n, a capacitor 23 and a connector 4, the connector 4
being connectable to a power source. According to this
invention, the memory board 2 retains stored data in the
volatile memories 21, 22 ...2n for a predetermined time
period even when the board 2 alone is disconnected from
the power source (not shown~.
Fig. 2 is a schematic diagram showing one embodiment of
the volatile memory hold device according to this invention,
which comprises a power source S, power terminals 25 and
25', a diode 27, a capacitor 23, a resistor 24, a display
26a, and volatile memories 21, 22 ...2n. The mode of
operation will hereinafter be explained, reference being made
to this schematic diagram. As the power source 5 supplies
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power terminals 25 and 25' with power, the power thus
supplied charges the capacitor 23 through the diode 27 and
the resistor 24, and, thence, energizes the memories 21 to
2n. When the power supply from the power source 5 is dis-
continued by disconnection of the source S from the terminals
25 and 25' or a malfunction of the source 5 such as an
interruption of electric power service, the capacitor 23
begins to discharge and supply the memories 21 to 2n with
the discharge power therefrom to keep the memories 21 to 2n
within the operating region thereof as long as the capacitor
23 holds a charged power at a level higher than a predeter-
mined power ~evel. The display 26a indicates that the power
supplied to the memories 21 to 2n is below a workable power
` level when the charge of the capacitor 23 is below the pre-
determined power level. A field effect type liquid crystal
display or an electrochronic device is suitable for the
display 26a, since it requires only a very small operating
; current. It has been confirmed on examination that C MOS
8K-bits-RAM having 16 chips requires 80 ~A when the R~M
changes the stored data, i.e., in dynamic status, but the
RAM requires only 1 ~A when the stored data are not changed,
i.e. static status. Accordingly, if the capacitor 23 has
a capacity value of 1000 ~F, it allows the memories 21 to
2n in static status to retain stored data for more than
24 hours. In other words, it is possible to retain stored
data in memories when the memory board 2 is disconnected
from an associated electronic system for more than 24
hours. The period of 24 hours is sufficient for usual
maintenance service. The diode 27a is provided for t~e
- 30 purpose of blocking the flow of an electric current from
the capacitor 23 to the terminals 25 and 25'. The diode
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27a prevents the capacitor 23 from instantly discharging -
through any external low impedance load across the terminals
25 and 25'. The external low impedance load may arise from
~-~ a malfunction of the power source 5 or a short connection
- between terminals 25 and 25'. The resistor 24 is designed
with a resistance rating such that on saturation of the
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memories 21 to 2n, the discharge current from the capacitor
23 brings the memories 21 to 2n into a cut-off region. If
the memories 21 to 2n are saturated with an external noise
in the absence of a power supply from the source 5, the
discharge current from the capacitor 23 is urged to flow to
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the memories as a rush current (about 10 mA~. However, such
a rush current is effectively blocked by the resistor 24
which, as noted, has a high rated resistance.
The resistor 24 returns the memories 21 to 2n into the
operating region from the saturating region without a large
` consumption o-f the discharge power from the capacitor 23.
This automatic return of the memories 21 to 2n into the
normal operating region prevents an error when stored data
in the memories are processed again. The display 26a also
indicates if stored data are properly retained in the
memories 21 to 2n which are supplied by the discharge power
from the capacitor 23, and prevents error in data processing
when the memory board 2 having memories 21 to 2n is again
mounted in an associated electronic system.
Fig. 3 is a schematic diagram showing another embodiment
of the vola~ile memory hold device, which includes a re-
; chargeable battey 3 as a supplemental power source of the
source 5, battery terminals 26 and 26 r ~ a diode 2~ and a
resistor 27. The battery 3 is charged through the resistor
27 by the power from the source 5, and discharges through
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the diode 28 and memories 21 and 2n when the power from thesource S is not available. The capacitor 23 will supply
the memories 21 to 2n with the discharge power when the
power from the source S and battery 3 are both no longer
available.
Fig. 4 is a schematic diagram of another embodiment of
- a volatile memory hold dev~ice which is an improvement over
^ the device of Fig. 3. The rechargeable battery 3 is charged
through resistor 41, a diode 42 and a resistor 45 by the
power from the source 5. The battery 3 discharges through a
diode 44, memories 21 to 2n and resistor 45. The resistor
24 and the diode 27a have the same function and effects as
in Fig. 2.
Fig. 5 is a schematic diagram of another embodiment of
a volatile memory hold device which includes a non-recharge-
able batter~ 50. The voltage of the battery S0 ïs set to
be below the voltage of the source 5. The diode 51 blocks
the flow of a current from the source S to the battery S0
and causes the battery S0 to supply memories 21 to 2n with
the discharge power thereof when the power from the source 5
is no longer available. It will be apparent that the
capacitor 23 supplies memories 21 to 2n with the discharge
power from the capacitor 23 when the power from the source S
and the battery 50 are both unavailable. A display 54 will
indicate that the voltage of the battery 50 is below a pre-
determined level and the battery .nust then be replaced.
Fig. 6 is a schematic diagram of another embodiment of
the volatile memory hold device accord;ng to this invention
which includes a Zener diode 61 and a resistor 60, in
addition to power source 5, terminals 25 and 25', capacitor
23, resistor 24, display 26a and memories 21 to 2n. ~ig. 7
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is a graph for explaining the embodiment of Fig. 6, which
shows a discharge voltage appearing across the two electrodes
of the capacitor 23. In normal operation, the rated voltage
Vo of the power source 5 drops through a voltage drop
- resistor 60 to a predetermined voltage Vz which is dictated
by the Zener voltage of the Zener 61 and is above the minimum
operating supply voltage for the memories 21 to 2n. The
resistor 60 has a low resistance to allow the diode 61 and
memories 21 and 2n to work. The capacitor 23 is charged up
to the same voltage level as Vo. When the power supply
from the power source 5 is not available, the capacitor 23
starts discharging along the curve 70 in Fig. 7. The curve
71 is an exponential curve which the capacitor 23 without
load will trace. The resistor 24 has a sufficient resistance
to allow a sufficient current to be supplied to the memories
21 to 2n to retain stored data therein. The voltage Vc
appearing across the two electrodes of the capacitor 23
drops rather sharply to Vz from Vo since some current flows
to the Zener diode 61 from the capacitor 23 as long as the
voltage Vc is over the Zener voltage. But the subsequent
discharge curve of the capacitor 23 below the Voltage Vz
shows a slowing of the discharge, since there is no current
through the diode 61 from the capacitor 23 and the discharge
current is only applied to the memories 21 to 2n in the
order of micro amperes which is very close to a natural dis-
` charge current of the capacitor 23. Consequently, the time
period before the voltage Vc drops to the voltage Vt where
the discharge curve 70 is flattened may be fairly extended~
The voltage Vt is set to be above the minimum operational
supply voltage of memories 21 to 2n. According to this
embodiment, therefore, the volatile memory hold device may
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retain stored data therein by the capacitor discharge alonefor many more hours than the period which is obtained by any
: of the preceding embodiments.
,
.~ According to one aspect of construction of this invention,
a volatile memory is supplied with sufficient power to retain
:` stored data therein for many hours even when a sustained
interruption of power service takes place of the power supply
. from a power source including a supplemental power source
such as a battery is not available.
, 10 It should be understood that the above description is
:. merely illustrative of this invention and that many changes
and modifications may be made by those skilled in the art
without departing from the scope of the appended claims.
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