JPH0487532A - Electronics - Google Patents

Abstract

PURPOSE:To realize space saving and cost reduction on the body side and cost reduction of an IC card by providing a voltage detecting circuit for a backup battery in the IC card thereby eliminating an A/D converting circuit on the body side and substituting a small and inexpensive voltage detector for a large and expensive reset IC. CONSTITUTION:In a detachable IC card as an external memory, a voltage detector detects the output voltage of a backup battery Bat. When the operating voltage on the body side drops below a predetermined level, the voltage detector 13 brings a RAM 11 into standby state. Consequently, the voltage detector on the side of the IC card can detects the output voltage of the backup battery without requiring an A/D converting circuit on the body side. Furthermore, a small and inexpensive voltage detector can be substituted for a large and expensive reset IC on the card side, resulting in space saving and cost reduction on the host side and cost reduction of the IC card.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention uses a removable IC card as an electronic device, particularly an external storage device, and supplies power to the IC card from the device body during the period when the IC card is installed. The present invention relates to an electronic device in which, when the IC card is removed, the storage contents of the memory element of the IC card are backed up by a backup power supply element within the IC card.

[Prior Art] Traditionally, electronic devices, especially handheld terminals, portable word processors, and personal computers, have been used.
Devices that use IC cards as storage media are known. In this type of device, a structure is known in which data on the memory is retained by a backup battery built into the memory card when the memory card is not installed in the device.

The circuit diagram of a conventional IC card with a backup battery is shown in FIG. In FIG. 3, reference numeral 31 denotes a RAM (usually S-RA) as a storage medium of the card.
In M), the storage contents are backed up by the output of the backup battery Bat via the control IC 32 (ICI). Also, the voltage of the backup battery Bat is the resistance R
1 to the host electronic device, and this voltage can be detected on the host side.

In FIG. 3, IC32 is usually called a reset IC, and connects the higher voltage of the power supply V DOl from the host side and the backup battery Bat output to the card power supply voltage V
It is supplied to the RAM 31 as DO2.

In addition, when the voltage of VDDI falls below a predetermined value and interrupts the operating voltage, IC32 sets the R5T voltage to a low level and R
The analog switch 33 (IC2) that controls the chip of AM31 and the write enable signal bus is turned off, and the RAM 31 is placed in a standby state.

[Problems to be Solved by the Invention] In the above conventional example, a voltage detection circuit (usually A-
D conversion circuit), which has the drawback of increasing the mounting area and cost of the host. Further, the reset IC 32 shown in FIG. 3 is relatively expensive and the size of the IC is also large.

An object of the present invention is to solve the above problems.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a removable IC card is used as an external storage device, and power is supplied from the main body of the device to the IC card during the period when the IC card is installed. In electronic equipment where the memory contents of the IC card's memory element are backed up by the backup power supply element inside the IC card when the IC card is removed after
a voltage detection circuit, a control means for supplying a higher voltage of the bias voltage supplied from the backup power supply element or the device main body as an input voltage to the voltage detection circuit, and inputting the pressure of the voltage detection circuit to the device main body side. A structure consisting of means was adopted.

[Function] According to the above configuration, the output voltage of the backup battery can be detected by the voltage detector on the IC card side without requiring an A/D conversion circuit on the host side.

[Example] Hereinafter, the present invention will be described in detail based on the example shown in the drawings.

FIG. 1 shows the structure of an electronic device adopting the present invention.

In FIG. 1, the symbol Bat indicates a backup battery as in FIG. 3, and the voltage of the backup battery Bat is i
f Through a resistor R1 and a diode D2 for limiting the current,
The power supply voltage VDO2 of the card is supplied, and the output of the backup battery Bat is inputted to the voltage detector IC4 via the diode D3.

The source voltage vDD1 is the power from the host, and is supplied as the card's power supply voltage VDO2 via the diode Di. At this time, since the cathodes of the diodes Dl and D2 are coupled together, the output of the backup battery Bat or the host's power supply voltage VDDI, whichever is higher, is supplied as the card's power supply voltage VDO2.

In this embodiment, symbols 13j5 and 14 (IC3 and IC
4) is a voltage detector, and when the operating voltage of the host becomes lower than a predetermined value, the voltage detector 13 sets the output voltage Vo to a low level and shuts off the analog switch of IC2. The analog switch 12 controls the RAM II chip and write enable signal buses (CE, WE: bars in the figure indicate negative logic active). Since the voltage detector I3 does not require reset input control, it can be configured with a simple comparator or the like.

When the analog switch 12 is turned off, the chip enable voltage CE and write enable voltage WE of RAMII are pulled up by R2 and R3, so the RAM II enters a standby state. The voltage detector 14 in the detection circuit 16 is a voltage detector for detecting whether the output voltage of the backup battery Bat has become below a predetermined value.

Here, if the power supply voltage of the circuit is 5V, the voltage detector 1
4, a bias circuit is provided in the detection circuit 16 because the output becomes unstable near Ov<(1.5V or less).

In the detection circuit 16, the code Q1. Q2 is a switching transistor. Here, transistor Q1. Q2
．． Resistors R3, R4, R5 and Zener diode Z
D is for forming a bias voltage input to the voltage detector 14 from the power supply voltage VDDI (or another voltage) on the main body side.

The host device outputs a low level signal to the voltage DET when detecting the voltage of the backup battery of the IC card, and reads the logic level of the LB voltage after a predetermined time.

When a low level is input from the voltage DET, the transistor Ql is turned on, and current flows into the Zener diode ZD through the resistor R4. The Zener voltage of the Zener diode ZD is selected to be higher than the operating voltage of the voltage detector 14 and lower than the memory backup voltage.

Since the Zener voltage is inputted to the voltage detector 14 via D4, the higher of the output voltage of the backup battery Bat and the Zener voltage becomes the input voltage of the voltage detector 14.

V BAT in FIG. 2 indicates the output voltage of the backup battery Bat, and here 2.5v is the threshold for memory backup.

The voltage detector 14 outputs an output voltage vO as long as the voltage of the backup battery Bat is sufficient for memory backup.
to high level or oven (high impedance) state. At this time, even if the host applies a low level from the voltage DET, the output of the voltage LB remains at a high level.

On the other hand, when the voltage of the backup battery Bat becomes insufficient as a memory backup voltage, a low level is output from the output voltage vo.

At this time, a base current flows through the transistor Q2 through the transistor Q1 and the resistor R5, pulling the voltage LB to a low level (see Fig. 2). Also, whether the backup battery Bat is removed or
When the capacitance becomes 0, the bias voltage is applied to the voltage detector 14.
Similarly, the LB voltage becomes low level.

In this manner, the host side can read the level of the voltage LB after setting the voltage DET to low and determine the voltage of the backup battery.

At this time, if the LB voltage is at a low level, it can be determined that the voltage of the backup battery has decreased, so in this case, a warning may be issued to the user by issuing a buzzer or a visible display.

Note that since the Zener current is relatively large, the host side
It is advisable to set the voltage DET to a high level immediately after reading the state of the B voltage to suppress wasteful current consumption.

According to the above embodiment, by providing a backup battery voltage detection circuit in the IC card, the host side A/D
No need for a conversion circuit. In addition, the expensive and large-sized reset IC can be replaced with the inexpensive and small-sized voltage detector 13, making it possible to save space and cost on the host side and reduce the cost of the IC card.

Furthermore, according to the above embodiment, the voltage on the host side is divided to create a bias voltage, and the higher of this bias voltage and the voltage of the backup battery is input to the voltage detector 14, so that the capacity of the backup battery is exhausted. It has the advantage that voltage can be detected even when it is disconnected or disconnected.

In the above embodiment, an example was explained in which a Zener diode was used to generate the bias voltage, but as shown in FIG. 4, almost the same effect can be obtained by using a voltage divided by the resistors R4 and R6. .

However, the values of the resistors R4 and R6 are set so that the partial voltage thereof is greater than or equal to the maximum operating voltage of the voltage detector 14 and less than or equal to the backup holding voltage.

[Effects of the Invention] As is clear from the above, according to the present invention, a removable IC card is used as an external storage device, and an IC card is used as an external storage device.
In electronic equipment, power is supplied from the device itself to the IC card during the card installation period, and when the IC card is removed, the contents of the memory element of the IC card are backed up by the backup power supply element inside the IC card. , a control means for supplying a higher voltage of the bias voltage supplied from the backup power supply element or the device main body as an input voltage of the voltage detection circuit, and a means for manually inputting the output of the voltage detection circuit to the device main body. , the output voltage of the backup battery can be detected by the voltage detector on the IC card side without requiring an A/D conversion circuit on the main body side. In addition, the expensive and large-sized reset IC on the card side can be replaced with an inexpensive and small-sized voltage detector, making it possible to save space and cost on the host side and reduce the cost of the IC card.
Furthermore, it has excellent effects such as being able to detect the voltage even when the backup battery has run out of capacity or has been removed.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an IC card embodying the present invention, Fig. 2 is a timing chart showing the operation of Fig. 1, Fig. 3 is a circuit diagram showing a conventional configuration, and Fig. 4 is another implementation. FIG. 3 is a circuit diagram showing an example. 12--Analog switch 13.14--Voltage detector Ql, Q2--Transistor D1-D4--Diode ZD--Zener diode R1-R6--Resistance Bat--Memory backup battery RAM --・Static RAM

Claims (1)

[Claims] 1) A removable IC card is used as an external storage device, and during the period when the IC card is installed, the IC card is not removed from the main body of the device.
In electronic equipment where the contents of the memory element of the IC card are backed up by the backup power supply element inside the IC card when power is supplied to the card and the IC card is removed, the input voltage of the voltage detection circuit and this voltage detection circuit is An electronic device comprising: a control means for supplying a higher voltage among the bias voltages supplied from the backup power supply element or the device main body; and a means for inputting the output of the voltage detection circuit to the device main body.