JP2000148390A - Coordinate input device adaptable to usb suspend mode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coordinate input device adaptable to a USB suspend mode that reduces the current consumption in the suspend mode and does not impair the responsiveness during the time in the suspend mode. SOLUTION: Light emitting diodes 16 and 18 of X, Y axis encoders 21 and 22 are serially connected and are connected with a DC current source Vcc via a first current control circuit 24 and a second current control circuit 25. When a measured value of a counter in a control part 23 is changed, the coordinate input device is regarded as in a normal mode and the current is supplied to the light emitting diodes 16, 18 via the first current control circuit 24. When the measured value of the counter in the control part 23 is not changed, the coordinate input device is regarded as in the suspend mode and the current to be supplied to the light emitting diodes 16, 18 is reduced by the second current control circuit 25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a USB (Universal)
More particularly, the present invention relates to a USB suspend mode compatible coordinate input device capable of reducing current consumption in the suspend mode and shortening the time for releasing the suspend mode.

[0002]

2. Description of the Related Art In a personal computer (PC), G
A UI (Graphical User Interface) has become mainstream, and a coordinate input device such as a mouse or a trackball is used to operate a cursor on a display. As these coordinate input devices, the operation amount is decomposed into X-Y components orthogonal to each other and then the operation amount is detected by a rotary encoder, and the operation amount is detected by the number of times of traversing a grid drawn on a substrate. There is something to do.

FIG. 1 is a principle diagram of a conventional rotary encoder mouse, in which a ball 10 is rotated by a mouse operation by a user. An X-axis roller 11 and a Y-axis roller 12 are arranged so as to contact the ball 10 along an X-axis and a Y-axis orthogonal to the ball 10. An X-axis rotary encoder 21 and a Y-axis rotary encoder 22 are attached to tips of the X-axis roller 11 and the Y-axis roller 12.

The X-axis rotary encoder 21 stores the X-axis slit disk 13 and the X-axis light-emitting elements 16 and the X-bearing light elements 17 arranged on both sides thereof. Is output. The Y-axis rotary encoder 22 stores the Y-axis slit disk 14 and the Y-axis light-emitting elements 18 and the Y-bearing light elements 19 disposed on both sides of the Y-axis slit disk 14, and outputs a number of pulses proportional to the Y-axis direction operation amount. Output.

[0005] In order to maintain the contact between the ball 10 and the X-axis roller 11 and the Y-axis roller 12, a pressing roller 15 is provided in a direction of 45 degrees with respect to the X-axis and the Y-axis. Most of the power consumption of the rotary encoder mouse is based on the X-axis light-emitting element 16 and the Y-axis light-emitting element 1.
8, the switching of the current supplied to both light emitting elements is performed in order to reduce current consumption and to expand the operating range irrespective of variations between the light emitting elements and the light receiving elements.

[0006]

However, in recent years, USB has been used as a connection standard between a PC and peripheral devices such as a coordinate input device.
(Universal Serial Bus) standard was proposed, but USB
In order to comply with the standard, it is necessary to reduce the current consumption when the peripheral device is not used, that is, when the peripheral device is in the suspend mode, to 500 μA or less.

However, in the coordinate input device, since 80% of the total current consumption is consumed for light emission by the light emitting element, it is essential to reduce the current consumption of the light emitting element in the suspend mode. In order to reduce the current consumption of the light-emitting element during the suspend mode, it is conceivable to increase the off-time of the switching current and reduce the temporal average current. There is a problem that the responsiveness is deteriorated when the user operates the coordinate input device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a USB suspend mode compatible coordinate input device capable of reducing current consumption in a suspend mode and shortening a time for releasing the suspend mode. The purpose is to do.

[0009]

Means for Solving the Problems USB according to the first invention
Suspend mode compatible coordinate input device, light emitting means, light flux control means for controlling the light flux emitted from the light emitting means in response to movement of the coordinate input device, light receiving means for receiving the light flux controlled by the light flux control means, Counting means for counting the number of pulses output when the output of the light receiving means is equal to or greater than a predetermined amplitude; and setting the coordinate input device to a suspend mode when the variation in the number of pulses counted by the counting means is equal to or less than a predetermined value. A control unit that sets the coordinate input device to the normal mode when the coordinate input device is in the normal mode when the coordinate input device is in the normal mode when the coordinate input device is set to the suspend mode by the control unit; Current reducing means for reducing the current supplied to the light emitting means when the operation is performed.

According to a second aspect of the present invention, in the coordinate input device corresponding to the USB suspend mode, the current reducing unit limits the voltage across the first current limiting resistor and the first current limiting resistor for limiting the current flowing to the light emitting unit. Current control means, comprising a first control transistor for controlling the current and a first switching transistor for cutting off the current supplied to the light emitting means in the normal mode, and arranged between the DC power supply and the light emitting means. And a second current limiting resistor having a resistance value larger than a resistance value of the first current limiting resistor for limiting a current flowing to the light emitting means, and a second voltage controlling both ends of the second current limiting resistor to be constant. A second switching transistor configured to control the current supplied to the light emitting means in the suspend mode and a second switching transistor connected in parallel to the first current control means; It comprises a flow control means.

In the coordinate input device for USB suspend mode according to a third aspect of the present invention, the current reducing means controls a current limiting resistor for limiting a current flowing to the light emitting means in the normal mode and a voltage across the current limiting resistor to be constant. Current control means comprising a control transistor and a switching transistor for cutting off current supplied to the light emitting means; first connection means for connecting a DC power supply and current control means in a normal mode; And second connection means for connecting the power supply and the current control means via a resistor having a predetermined resistance value.

According to a fourth aspect of the present invention, in the coordinate input device for USB suspend mode, the current reducing means is disposed between the light emitting means and the ground and limits the current flowing to the light emitting means in the normal mode. And a second current limiting resistor that is arranged in parallel with the first current limiting resistor and that has a resistance value larger than the resistance value of the first current limiting resistor that limits the current flowing to the light emitting unit in the suspend mode. .

In the first to fourth inventions, the current supplied to the light emitting element in the suspend mode is smaller than the current in the normal mode. A USB suspend mode-compatible coordinate input device according to a fifth aspect of the present invention includes a light emitting unit, a light beam control unit that controls a light beam emitted from the light emitting unit in accordance with the movement of the coordinate input device, and a light beam controlled by the light beam control unit. A light receiving means for receiving light; a counting means for counting the number of pulses output when the output of the light receiving means is equal to or greater than a predetermined amplitude; A change detecting means for detecting a change in output; and a suspend mode when the change in the number of pulses counted by the counting means is equal to or less than a predetermined value or when no change in the output of the light receiving means is detected by the change detecting means. When the change in the number of pulses counted by the counting means is equal to or more than a predetermined value or when the change in the output of the light receiving means is detected by the change detecting means, the coordinate input device is normally operated. Comprising a control means for the over-de, a.

A USB suspend mode compatible coordinate input device according to a sixth aspect of the present invention includes a light receiving element in which a light receiving means is connected to the change detecting means. According to a seventh aspect of the present invention, there is provided a USB suspend mode compatible coordinate input device, wherein the controller supplies current to the light emitting unit when the coordinate input device is set to the suspend mode when the control unit sets the coordinate input device to the normal mode. The apparatus further includes a current reducing unit that reduces the current supplied to the light emitting unit.

According to an eighth aspect of the present invention, in the coordinate input device for USB suspend mode, the current reducing means limits the current flowing through the light emitting means to a first current limiting resistor and a voltage across the first current limiting resistor. Current control means, comprising a first control transistor for controlling the current and a first switching transistor for cutting off the current supplied to the light emitting means in the normal mode, and arranged between the DC power supply and the light emitting means. And a second current limiting resistor having a resistance value larger than a resistance value of the first current limiting resistor for limiting a current flowing to the light emitting means, and a second voltage controlling both ends of the second current limiting resistor to be constant. A second switching transistor configured to control the current supplied to the light emitting means in the suspend mode and a second switching transistor connected in parallel to the first current control means; It comprises a flow control means.

According to a ninth aspect of the present invention, in the USB input device corresponding to the USB suspend mode, the current reducing means controls a current limiting resistor for limiting a current flowing to the light emitting means in the normal mode and a voltage across the current limiting resistor to be constant. Current control means comprising a control transistor and a switching transistor for cutting off current supplied to the light emitting means; first connection means for connecting a DC power supply and current control means in a normal mode; And second connection means for connecting the power supply and the current control means via a resistor having a predetermined resistance value.

According to a tenth aspect of the present invention, in the USB input device corresponding to the USB suspend mode, the current reducing means is disposed between the light emitting means and the ground and limits the current flowing to the light emitting means in the normal mode. And a second current limiting resistor that is arranged in parallel with the first current limiting resistor and that has a resistance value larger than the resistance value of the first current limiting resistor that limits the current flowing to the light emitting unit in the suspend mode. .

In the fifth to tenth aspects, the operation in the suspend mode is quickly detected.

[0019]

FIG. 2 is a circuit diagram of a mouse as a coordinate input device according to the first invention. The X-axis rotary encoder 21 includes an X-axis light emitting element 16, an X-axis slit disk 1
3, and two phototransistors 171 and 172 constituting the X-bearing optical element 17, and the two phototransistors 171 and 17 block the transmission and blocking of light emitted from the X-axis light-emitting element 16 by the X-axis slit disc 13.
The number of pulses detected in step 2 is proportional to the amount of rotation of the ball 10 in the X-axis direction.

The Y-axis rotary encoder 21 includes a Y-axis light emitting element 17, a Y-axis slit disk 14, and two phototransistors 191 and 192 constituting a Y-bearing optical element 19. The blocking and transmission of light emitted from the light source 17 are detected by two phototransistors 191 and 192, and the ball 10
Are output in a number proportional to the rotation amount in the Y-axis direction.

The control unit 23 is a microprocessor system, and has an output port 232,
Counter 233, input port 234, interrupt port 2
35, a memory 236, and a CPU 237. The anode of the X-axis light-emitting element 16 is connected to the DC power supply bus _Vcc via the first current control circuit 24 and the second current control circuit 25 connected in parallel with each other,
The cathode is connected to the anode of the Y-axis light emitting element 18.
The cathode of the Y-axis light emitting element 18 is grounded.

The first current control circuit 24 keeps the voltage across the current limiting resistor 241 and the current limiting resistor 241 for regulating the current flowing through the X-axis light emitting element 16 and the Y-axis light emitting element 18 constant. Axis light emitting element 16 and Y
It is composed of a current control transistor 242 that controls the current flowing through the axis light emitting element 18 and a switching transistor 243 that cuts off the current flowing through the X axis light emitting element 16 and the Y axis light emitting element 18.

The configuration of the second current control circuit 25 is the same as that of the first current control circuit 24, but the second current control circuit 2
Resistance of the current limiting resistor 251 5 (R _2), the resistance value of the current limiting resistor 241 of first current control circuit 24 (R ₁₎
It is set larger, that is, R ₁ <R ₂ . Then, the switching transistor 24 of the first current control circuit 24
3 is controlled by a control signal output from the output port 232 during normal operation, and the ON / OFF of the switching transistor 253 of the second current control circuit 25 is controlled by a control signal output from the output port 232 in the suspend mode. .

Further, a connection point between a third resistor 261 having one end connected to the DC power supply bus _Vcc and a capacitor 262 having one end grounded is connected to the interrupt port 234.
Accordingly, since an interrupt pulse is generated at the interrupt port 234 for each time constant that is a function of the resistance value of the third resistor 261 and the capacitance of the capacitor 262, the control unit 23 in the suspend mode is interrupted by the interrupt pulse every time. The suspend mode is released.

The collectors of the two phototransistors 171 and 172 constituting the X-bearing optical element 17 are connected to the DC power supply _Vcc , and the emitters are connected to the input port 234. The collectors of the two phototransistors 191 and 192 constituting the Y-bearing optical element 19 are connected to a DC power supply _Vcc .
The emitter is connected to input port 234. Click switches 271 and 272 mounted on the coordinate input device are also connected to the input port 234.

FIGS. 3A and 3B are explanatory diagrams of the operation of the mouse which is the coordinate input device according to the first invention.
And 18, the solid line represents the current waveform supplied under the control of the first current control circuit 24 in the normal state, and the broken line represents the current waveform supplied by the second current control circuit 25 in the suspend mode. Represents a current waveform supplied under the condition (1).

That is, since R ₂ <R ₁ is set as described above, the pulse height in the suspend mode is lower than the pulse height in the normal mode. (B) is an X-bearing optical element 171,
172 (or the Y-bearing optical elements 191 and 192), the solid line represents the output in the normal state, and the broken line represents the output in the suspend mode. (C) is a pulse waveform read at the input port 234, which is obtained by pulsing the waveform of (b) using a threshold value.

As can be seen from the figure, in the suspend mode, the pulse height becomes low and the rise of the output of the light emitting element becomes slow, so that reading of the pulse via the input port 234 becomes slow, but it is in the suspend mode. This delay is not a problem. In the suspend mode, the pulse height value is low, so that the current consumption in the suspend mode is reduced.

FIG. 4 is a flowchart of a first control routine executed by the control unit 23.
It is executed every time an interrupt pulse is generated at 34. In step 41, the count value of the counter 233 incorporated in the control unit 23 is read, and in step 42, the operation states of the click switches 271 and 272 are read.

In step 43, it is determined whether the coordinate input device has been operated, that is, whether the count value has changed by a predetermined amount or more, or whether the state of the click switch has changed. When an affirmative determination is made in step 43, that is, when it is determined that the coordinate input device has been operated, a counter OP indicating a period during which the coordinate input device is not operated is reset in step 44.

Next, at step 45, a drive command to the first current control circuit 24 is output from the output port 232. Then, in step 46, the process waits until the normal sampling period is reached.
Return to 1. Conversely, when a negative determination is made in step 43,
That is, when it is determined that the coordinate input device is not operated, the counter OP is incremented in step 47. The count value of the counter OP in step 48 determines whether a threshold OP _MAX than the predetermined.

If a negative determination is made in step 48, that is, if only a short time has elapsed after the coordinate input device is no longer operated, the process proceeds to step 45 assuming that it is too early to shift to the suspend mode. Step 4
If an affirmative determination is made in step 8, that is, if a certain amount of time has elapsed since the coordinate input device was no longer operated, the second current control circuit 25 is output from the output port 232 in step 49.
Is output, and this routine ends.

FIG. 5 is a circuit diagram of a mouse which is a coordinate input device according to the second invention, and only points different from the first coordinate input device will be described. That is, in the present embodiment, only one current control circuit 24 is provided, and the current control circuit 24 is connected to the DC power supply _Vcc via the first transistor 28 and the series connection of the resistor 291 and the second transistor 292. You.

That is, normally, the first transistor 28 is turned on by an operation command output from the output port 232, and the current control circuit 24 is supplied to the light emitting elements 16 and 18 because it is directly connected to the DC power supply _Vcc. The current is large. Conversely, in the suspend mode, the second transistor 292 is operated by an operation command output from the output port 232.
Is turned on, and the current control circuit 24 is connected to the DC power supply _Vcc via the resistor 291.
Is small.

FIG. 6 is a flow chart of a second control routine executed by the control unit 23. In the first control routine, Step 6 is replaced with Step 6 instead of Steps 45 and 49.
Steps 5 and 69 are executed. That is, when it is determined that the coordinate input device has been operated, an ON command is output to the first transistor 28 and a drive command to the current control circuit 24 is output in step 65.

If it is determined that the coordinate input device has not been operated, then at step 69 the second transistor 292
And outputs an ON command to the current control circuit 24.
Is output. FIG. 7 is a circuit diagram of a mouse which is a coordinate input device according to the third invention. The second coordinate input device has a first transistor 28 and a resistor 291 arranged on the DC power supply _Vcc side and a second transistor. Transistor 2
A series connection of 92 is provided on the ground side.

In this embodiment, the second control routine can be applied as it is. In the above embodiment, although the power consumed by the light emitting element during the suspend mode can be reduced, the time until the change in the count value of the counter for detecting the rotation amount of the ball 10 is detected, that is, the suspend mode is released. Time cannot be reduced. A coordinate input device according to the following invention aims to reduce the time during which the suspend mode is canceled.

FIG. 8 is a circuit diagram of a mouse which is a coordinate input device according to the fourth invention. In the X-axis rotary encoder 21 and the Y-axis rotary encoder 22, third phototransistors 173 and 193 are provided. An additional third phototransistor 173 and 193
Is connected to the A / D converter 238 in the control unit 23.

FIGS. 9A and 9B are internal configuration diagrams of the X-axis rotary encoder used in this embodiment. FIG. 9A is a front sectional view, and FIG. 9B is a bottom sectional view. Note that the Y-axis rotary encoder 22 has a similar configuration. That is, the output of the third phototransistor 173 is output from the A / D converter 23.
Since it is converted into a digital value at step 8, it is possible to detect even a slight movement of the X-axis slit disk 13.

Accordingly, if the suspend mode is released by a change in the output of the A / D converter 238, the time required for releasing from the suspend mode can be reduced. FIG.
This is a third control routine executed by the control unit 23 in the coordinate input device according to the present invention, wherein step 101 is inserted between step 42 and step 43.

Then, in step 101, the output of the A / D converter 238 is read, and in step 43, the output of the A / D converter 238 is read.
Even when the output of the D converter 238 changes, it is determined that the operation of the coordinate input device has been performed, and the suspend mode is canceled in step 44. In the coordinate input device according to the fourth invention, it is necessary to store three phototransistors in the rotary encoder. However, in the coordinate input device according to the fifth invention, the release time from the suspend mode can be reduced without changing the two phototransistors. It is something to shorten.

FIG. 11 is a circuit diagram of a mouse which is a coordinate input device according to the fifth invention. One output of two phototransistors in a rotary encoder is supplied not only to an input port 234 but also to an A / D converter 238. Is also connected. Note that the coordinate input device according to the fifth invention is also controlled by the third control routine. The fourth or fifth aspect of the present invention may be applied to the coordinate input device according to the first to third aspects of the present invention to reduce the current consumption during the suspend mode and to shorten the time for releasing from the suspend mode. It becomes possible.

The coordinate input device of the type in which the amount of movement is detected by the rotary encoder has been described above.
The coordinate input device emits light toward the moving substrate, detects reflected light from the substrate, and detects the number of movements across the grid drawn on the substrate to detect the amount of movement. The present invention can also be applied to this.

[0044]

According to the USB suspend mode compatible coordinate input device according to the first to fourth aspects of the present invention, the current supplied to the light emitting element in the suspend mode is made smaller than the current in the normal mode, thereby enabling the suspend mode. Current consumption can be reduced.

According to the USB suspend mode-compatible coordinate input device of the fifth to tenth aspects, it is possible to quickly detect that the coordinate input device has been operated, thereby reducing the time required until the suspend mode is released. It can be shortened.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of a conventional mouse.

FIG. 2 is a circuit diagram of the mouse according to the first invention.

FIG. 3 is an explanatory diagram of an operation of the mouse according to the first invention.

FIG. 4 is a flowchart of a first control program.

FIG. 5 is a circuit diagram of a mouse according to the second invention.

FIG. 6 is a flowchart of a second control program.

FIG. 7 is a circuit diagram of a mouse according to a third invention.

FIG. 8 is a circuit diagram of a mouse according to a fourth invention.

FIG. 9 is an internal configuration diagram of an X-axis rotary encoder.

FIG. 10 is a flowchart of a third control program.

FIG. 11 is a circuit diagram of a mouse according to a fifth invention.

[Description of Signs] 21 ... X-axis rotary encoder 13 ... X-axis slit disk 16 ... X-axis light emitting diode 171,172 ... X-axis phototransistor 22 ... Y-axis rotary encoder 14 ... Y-axis slit disk 18 ... Y-axis light emitting diode 191 , 192: Y-axis phototransistor 23: control unit 24: first current control circuit 25: second current control circuit

Claims (10)

[Claims] A light emitting unit; a light beam controlling unit that controls a light beam emitted from the light emitting unit in response to movement of a coordinate input device; a light receiving unit that receives a light beam controlled by the light beam controlling unit; Counting means for counting the number of pulses output when the output of the light receiving means is equal to or greater than a predetermined amplitude; and suspending the coordinate input device when the variation in the number of pulses counted by the counting means is equal to or less than a predetermined value. Control means for setting the coordinate input device to the normal mode when the value is equal to or more than a predetermined value; and a current supplied to the light emitting means when the coordinate input device is set to the suspend mode by the control means. And a current reducing unit that reduces the current supplied to the light emitting unit when the input device is in the normal mode. A first current limiting resistor that limits a current flowing through the light emitting unit; a first control transistor that controls a voltage across the first current limiting resistor to be constant. A first switching transistor that cuts off a current supplied to the light-emitting means in a normal mode, a first current control means disposed between a DC power supply and the light-emitting means, A second current limiting resistor having a resistance value larger than a resistance value of the first current limiting resistor for limiting a current flowing to the means, and a second current limiting device for controlling a voltage across the second current limiting resistor to be constant. A control transistor; and a second switching transistor that cuts off a current supplied to the light emitting unit in a suspend mode.
2. A USB suspend mode compatible coordinate input device according to claim 1, further comprising: a second current control means arranged in parallel with said current control means. 3. The current reducing means includes: a current limiting resistor for limiting a current flowing to the light emitting means in a normal mode; a control transistor for controlling a voltage across the current limiting resistor to be constant; Current control means comprising: a switching transistor for cutting off a current to be supplied; first connection means for connecting a DC power supply to the current control means in a normal mode; and DC power supply and the current control in a suspend mode. 2. The USB suspend mode compatible coordinate input device according to claim 1, further comprising: a second connection unit that connects the unit and the unit via a resistor having a predetermined resistance value. 4. A first current limiting resistor, which is disposed between the light emitting means and the ground, for limiting a current flowing through the light emitting means in a normal mode, and wherein the first current limiting resistor is provided. And a second current limiting resistor having a resistance value larger than a resistance value of the first current limiting resistor that limits a current flowing to the light emitting unit in a suspend mode. US
B suspend mode compatible coordinate input device. 5. A light emitting means; a light flux controlling means for controlling a light flux emitted from the light emitting means in response to movement of a coordinate input device; a light receiving means for receiving a light flux controlled by the light flux controlling means; Counting means for counting the number of pulses output when the output of the light receiving means is greater than or equal to a predetermined amplitude; and changing the output of the light receiving means even if the output of the light receiving means is less than or equal to the predetermined amplitude A change detection means for detecting, and when the change in the number of pulses counted by the counting means is equal to or less than a predetermined value, or when a change in the output of the light receiving means is not detected by the change detection means, the coordinate input device is suspended. And when the change in the number of pulses counted by the counting means is equal to or greater than a predetermined value, or when the change detecting means detects a change in the output of the light receiving means. USB Suspend mode corresponding coordinate input apparatus comprising a control means for the input device and the normal mode. 6. The USB input device according to claim 5, wherein said light receiving means includes a light receiving element connected to said change detecting means. 7. A current supplied to the light emitting means when the coordinate input device is set to the suspend mode by the control means, and is supplied to the light emitting means when the coordinate input device is set to the normal mode by the control means. The US according to claim 5 or 6, further comprising a current reducing means for reducing the current.
B suspend mode compatible coordinate input device. 8. A first current limiting resistor for limiting a current flowing to the light emitting unit, a first control transistor for controlling a voltage across the first current limiting resistor to be constant, and A first switching transistor that cuts off a current supplied to the light-emitting means in a normal mode, a first current control means disposed between a DC power supply and the light-emitting means, A second current limiting resistor having a resistance value larger than a resistance value of the first current limiting resistor for limiting a current flowing to the means, and a second current limiting device for controlling a voltage across the second current limiting resistor to be constant. A control transistor; and a second switching transistor that cuts off a current supplied to the light emitting unit in a suspend mode.
8. The USB suspend mode compatible coordinate input device according to claim 7, further comprising: a second current control means arranged in parallel with said current control means. 9. The current reducing means includes: a current limiting resistor for limiting a current flowing to the light emitting means in a normal mode; a control transistor for controlling a voltage between both ends of the current limiting resistor to be constant; Current control means comprising: a switching transistor for cutting off a current to be supplied; first connection means for connecting a DC power supply to the current control means in a normal mode; and DC power supply and the current control in a suspend mode. 8. The USB suspend mode compatible coordinate input device according to claim 7, further comprising: second connection means for connecting said means via a resistor having a predetermined resistance value. 10. A first current limiting resistor, which is disposed between the light emitting unit and the ground, and limits a current flowing through the light emitting unit in a normal mode. And a second current limiting resistor having a resistance value larger than a resistance value of the first current limiting resistor that limits a current flowing to the light emitting unit in a suspend mode. US
B suspend mode compatible coordinate input device.