JP2011118768A - Electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic device that earlier detects the connection of a USB peripheral. <P>SOLUTION: A USB interface circuit 36 is equipped with a current detection circuit 50 to be connected to a VBUS line. The current detection circuit 50 detects a current flowing in the VBUS line when an external recording medium 70 is connected, and supplies a drive current to the external recording medium 70. The current detection circuit 50 detects a rush current flowing when the external recording medium 70 is connected, and informs a system control circuit 30 that the external recording medium 70 has been connected via a bus 34. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electronic device, and more specifically to an electronic device that communicates a control signal or a data signal while supplying power to a peripheral device.

JP 2001-67156 A

  Conventionally, USB (Universal Serial Bus) is known as an interface for connecting peripheral devices to electronic devices. USB connects a plurality of peripheral devices (devices) to a host device (generally a computer) by serial communication. Japanese Patent Application Laid-Open No. 2004-151561 describes a technique related to a connection between a computer as a host device and a digital camera as a peripheral device.

  The USB has a plug and play function and a hot swap function. The plug-and-play function is a function for automatically recognizing and updating a connection relationship with a peripheral device when a peripheral device is newly connected or removed. The hot swap function is a so-called hot-swap function, and is a function that enables connection and removal of peripheral devices with the power turned on. The USB further has a function of supplying power to the peripheral device. With these functions, the user can use the peripheral device without being bothered by setting of the address and ID number and the power supply at the time of connection.

  The USB cable is composed of a total of four wires of a 5V power line called VBUS, a GND wire, and two signal wires D + and D−, and these are connected to the device by a dedicated connection terminal. Along with the connection, the host device supplies power to the peripheral device via the VBUS line. Thereafter, the peripheral device pulls up the D + line, and the host device recognizes the connection of the peripheral device by pulling up the D + line.

  According to the USB standard, the maximum time from connection to pull-up of the D + line is defined as 100 msec. However, many commercially available peripheral devices do not meet this standard. Therefore, although it is physically connected, it may take time for the host device to recognize the connection of the peripheral device.

  An object of this invention is to show the electronic device which eliminates such an inconvenience.

  An electronic device according to the present invention includes a connection unit that connects a peripheral device, a communication unit that communicates with the peripheral device via the connection unit, and a power supply unit that supplies power to the peripheral device via the connection unit And current monitoring means for monitoring the current supplied from the power supply means to the peripheral device, and the connection of the peripheral device is recognized when the current value by the monitoring means exceeds a threshold value. To do.

  According to the present invention, since the connection of the peripheral device can be detected by the drive current due to the connection of the peripheral device, the use of the peripheral device can be started quickly.

It is a schematic block diagram of one Example of this invention. 3 is a block diagram of a schematic configuration of a current detection circuit 50. FIG. It is a control flow figure at the time of picked-up image recording.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of an imaging apparatus according to an embodiment of the present invention. The imaging apparatus 10 can use an external recording medium 70 connected by a USB (Universal Serial Bus) cable 60 in addition to a recording medium (built-in recording medium) 24 built-in as a recording medium for captured images. The built-in recording medium 24 can be detached from the imaging device 10. The external recording medium 70 is a peripheral device for the imaging device 10 which is an electronic device serving as a host.

  A basic operation of the imaging apparatus 10 will be described. The taking lens 12 forms an optical image of the subject on the image sensor 14. The image sensor 14 converts an optical image from the photographing lens 12 into an electrical signal. The A / D converter 16 converts the analog image signal output from the image sensor 14 into a digital image signal. The camera signal processing circuit 18 performs known camera signal processing such as gamma correction, color balance adjustment, and color space conversion on the digital image signal from the A / D converter 16. The image data processed by the camera signal processing circuit 18 is stored in the memory 20 via the bus 34.

  As will be described later, the memory 20 is versatile for temporarily storing captured image data, for buffering in the case of continuous shooting, for processing by the compression / decompression circuit 22, for temporarily storing reproduced image data, and for image display. Used. Of course, it is clear that separate memories may be provided for these individual applications.

  The LCD drive circuit 26 reads out image data stored in the memory 20 at a constant cycle, and drives a liquid crystal display device (LCD) 28. As a result, an image corresponding to the optical image incident on the image sensor 14 is displayed on the screen of the LCD 28. In this state, the user can check the composition of the subject on the screen of the LCD 28, and the LCD 28 functions as a so-called electronic viewfinder. At this time, an image signal having a resolution sufficient for display on the LCD 28 is read from the image sensor 14.

  The user can input various instructions to the system control circuit 30 through the operation device 32, and the system control circuit 30 controls each unit according to the user's instructions and setting contents.

  For example, in response to a shutter release operation by the user, the captured image is compressed and recorded on the recording medium 24. That is, in response to the operation of the release button of the operation device 32, the image sensor 14 outputs an image signal having a resolution specified in advance (usually high resolution). The output image signal of the image sensor 14 is written into the memory 20 via the A / D converter 16, the camera signal processing circuit 18, and the bus 34. The compression / decompression circuit 22 compresses and encodes the captured image data stored in the memory 20. The image data compressed by the compression / decompression circuit 22 is supplied to the internal recording medium 24 via the bus 34 and stored in the internal recording medium 24. The built-in recording medium 24 is composed of, for example, a flash memory.

  In the playback mode, compressed image data of an image designated by the user is read from the built-in recording medium 24 and written to the memory 20 via the bus 34. A compression / decompression circuit 22 decompresses the compressed image data stored in the memory 20. Reproduced image data obtained by decompression of the compression / decompression circuit 22 is written back to the memory 20 via the bus 34.

  The LCD drive circuit 26 reads the reproduced image data in the memory 20 at a constant cycle, and drives a liquid crystal display device (LCD) 28. Thereby, the reproduced image is displayed on the screen of the LCD 28.

  The imaging apparatus 10 can designate the external recording medium 70 as a storage destination of the captured image. The connection configuration with the external recording medium 70 and the recognition operation of the external recording medium 70 by the imaging apparatus 10 will be described.

  The external recording medium 70 is connected to the imaging device 10 via the USB cable 60. For this USB connection, the imaging device 10 includes a USB interface circuit (or USB connection control device) 36 connected to the bus 34 and a USB connection terminal 38. As is well known, the USB cable 60 includes a VBUS line, a D + line, a D− line, and a GND line.

  The USB interface circuit 36 includes a host controller 40 that accommodates the D + line and the D− line, and includes an input / output buffer 42 for the D + line and an input / output buffer 44 for the D− line. The host controller 40 exchanges data packets with a USB device (here, the external recording medium 70). The D + line is connected to ground through a pull-down resistor 46, and the D− line is connected to ground through a pull-down resistor 48. In the USB standard, the host device side pulls down the D + line and the D− line.

  The VBUS line which is a power supply line is connected to the current detection circuit 50 and connected to the ground via the capacitor 52. The current detection circuit 50 functions as a power supply unit that supplies a drive current to a USB device to be connected (here, the external recording medium 70), and also functions as a current monitor unit that monitors the current value. Details of the current detection circuit 50 will be described later.

  The external recording medium 70 includes a USB connection terminal 72, a USB interface circuit (or USB connection control device) 74, and a hard disk 76. The USB interface circuit 74 includes a device controller 78 that accommodates the D + line and the D− line, and includes an input / output buffer 80 for the D + line and an input / output buffer 82 for the D− line. The device controller 78 exchanges data packets with the host controller 40. The VBUS line which is a power supply line is connected to the pro-up control circuit 84 and the device controller 78 to supply power. The VBUS line is connected to ground via a capacitor 86. The pull-up control circuit 84 raises the potential of the pull-up resistor 88 connected to the D + line to a predetermined value under power supply.

  FIG. 2 shows a schematic block diagram of a circuit example of the current detection circuit 50. In the circuit example shown in FIG. 2, a power switch IC 90 is used. The power switch IC 90 is a commercially available power switch IC having a function of detecting an overcurrent. The overcurrent detection function generally detects whether or not the current supplied from the host device to the peripheral device via the VBUS line exceeds an allowable value (threshold value). Many power switch ICs have an overcurrent detection function as well as an overcurrent detection function. There is also a power switch IC in which an allowable value can be arbitrarily set, and the allowable value is set by a resistance value of a resistor connected to the control terminal.

  The power switch IC 90 can set an overcurrent threshold value by the resistance value of the resistor connected to the control terminal. In the circuit shown in FIG. 2, a current detection value adjustment circuit 92 that can change the resistance value is connected. The power switch IC 90 is supplied with a power supply voltage (for example, 5 V) from the power supply terminal 94.

  In the illustrated example, the current detection value adjustment circuit 92 is configured such that the resistor 102 or 104 can be applied first by the switch 100. The resistance values of the resistors 102 and 104 are different from each other. For example, when the switch 100 is connected to the resistor 102, the current detection threshold is set to a high value, and when the switch 100 is connected to the resistor 104, the current detection threshold is set to a low value. When the USB device is not connected at all, the switch 100 is connected to the resistor 104 side. When the overcurrent detection function of the power switch IC 90 detects a current exceeding a certain level on the VBUS line, the switch 100 is switched to the resistor 102 side. In this state, an overcurrent during normal operation is detected.

  The power switch IC 90 also receives a control signal from the system control circuit 30 via the bus 34 and the control line 96 and notifies the system control circuit 30 of the current detection result via the current detection signal line 98 and the bus 34. Specifically, the system control circuit 30 can control on / off of the current output to the VBUS line in the power switch IC 90 via the control line 96. The power switch IC 90 also informs the system control circuit 30 of the overcurrent detection result using the set resistance value of the current detection value adjustment circuit 92 to the system control circuit 30 via the current detection signal line 98 and the bus 34. In this embodiment, using this function, the connection of the USB device can be detected at an early stage, and an overcurrent can be detected in the normal use state.

  FIG. 3 shows an example of a control method of the current detection value adjustment circuit 92. In an initial state where no peripheral device is connected, the resistor 104 is selected, and the threshold value of the current detection value is set to a low value (S1). When a peripheral device is connected (S2), a current detection interrupt is notified from the power switch IC 90 via the current detection signal line 98 (S3). The system control circuit 30 recognizes that the peripheral device is connected and permits release (photographing) (S4). Here, release permission is given as an example of processing after connection recognition, but it is obvious that other processing may be performed as needed after processing of connection recognition. Even if shooting is performed at this stage, the external recording medium 70 is not ready for recording. Accordingly, for shooting at this time, for example, the shot image data (or the compressed image data thereof) is temporarily stored in the memory 20 or the built-in recording medium 24.

  When the USB connection process (referred to as enumeration) is completed (S5), it is determined whether or not the connected USB device is an HDD, that is, the external recording medium 70 (S6). If it is not the HDD (S6), the user is warned by a warning display or the like (S7). If the connected peripheral device is an HDD (S6), the current detection value adjustment circuit 92 is switched from the resistor 104 to the resistor 102 (S8), and the power switch IC 90 is switched to the overcurrent detection function during normal operation (S8). . Thereafter, the external recording medium 70 is designated as the recording destination of the captured image (S9). If there is data temporarily stored in the memory 20 or the internal recording medium 24, the data is moved to the external recording medium 70.

  In this embodiment, the current flowing through the VBUS line is monitored, and when a current larger than the threshold value flows, it is determined that the peripheral device is connected. Thereby, the connection of the peripheral device can be recognized immediately together with the connection, and the use of the peripheral device can be prepared. Since an inrush current flows to the capacitor 86 when the external recording medium 70 is connected, the connection of the external recording device 70 can be immediately detected by monitoring the current of the VBUS line.

  Since the connection detection can be performed simultaneously with the connection, the host device can prepare for communication in advance even if the peripheral device is not ready for communication. As soon as the peripheral devices are ready, communication can be started immediately and the connection process can be sped up. For example, assuming that the host device is a digital camera and the peripheral device is a hard disk as a recording medium, in the conventional example, the recording medium could not be recognized until a certain time has elapsed since the connection. In the example, since the peripheral device can be recognized at the same time as the connection, for example, release can be permitted.

Claims (3)

Connection means for connecting peripheral devices;
Communication means for communicating with the peripheral device via the connection means;
Power supply means for supplying power to the peripheral device via the connection means;
Current monitoring means for monitoring the current supplied from the power supply means to the peripheral device,
An electronic device characterized by recognizing connection of the peripheral device when a current value by the monitoring means exceeds a threshold value.   The electronic device according to claim 1, wherein the connection unit is a USB (Universal Serial Bus) connection terminal.   The electronic apparatus according to claim 1, wherein the electronic apparatus is an imaging device.

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