JP2004038411A - Data transferring method and data transferring system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize data transfer that is secure not only for a transmitting means which transmits data but also for a receiving side host terminal which receives data. <P>SOLUTION: At the time of transferring data from a digital camera 12 through communication lines 16 and 18 to a host PC 22, the value of the power supply voltage of the camera 12 is confirmed, and a data packet 60 applied with a flag 64 corresponding to the confirmed value of the power supply voltage is transferred to the host PC 22. The flag 64 applied to the packet 60 is identified by the host PC 22, and an instruction packet 80 for changing the transfer mode of the camera 12 is returned from the host PC 22 to the camera 12 according to the identification result. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a data transfer method and a data transfer system from a transmission means to a receiving host terminal.
[0002]
[Prior art]
Devices that perform data transfer must not run out of battery during data transfer. If the battery runs out during data transfer or the power supply becomes unstable, the data transfer may not be completed due to an error, or the storage device such as flash memory in the device may be damaged and data may be lost. Because there is sex. If the data is destroyed in this way, there is a possibility that the transmitting means or the receiving host terminal cannot subsequently perform an appropriate operation.
[0003]
In order to solve such a problem, Japanese Patent Laid-Open No. 10-307684 discloses a warning message when a charge amount of a drive is reduced while data is being transmitted from a floppy disk drive to the host computer by infrared communication. Send it to a computer for display. Thereby, the necessity of charge is understood. Japanese Patent Application Laid-Open No. 11-65948 is a technique for transmitting data to the outside of the terminal via wireless communication means when the battery level of the portable information terminal is low, and to protect the data with certainty. Further, according to Japanese Patent Laid-Open No. 2001-86277, the remaining battery level is detected before image data is transmitted from the transmitter to the receiving side, so that interruption of data transmission is avoided.
[0004]
Thus, according to the prior art, before the data is transferred from the transmission unit to the receiving host terminal, the remaining battery level of the transmission unit is usually confirmed. This is because, as a result of the confirmation, it can be determined whether the data transfer can be completed to the end, or whether the data transfer cannot be completed due to the battery running out along the way. As a result, for example, as described in Japanese Patent Application Laid-Open No. 2001-86277, when the remaining amount of the battery is insufficient, a measure is taken to prohibit transmission of image data from the beginning.
[0005]
[Problems to be solved by the invention]
However, all of the countermeasures against the shortage of battery power found in the prior art are executed when the transmission means unilaterally stops data transfer when the battery power of the transmission means is short. This forcibly terminates data reception being executed on the host side, and may cause an abnormality on the host side.
[0006]
The present invention eliminates such drawbacks of the prior art, and even when the power supply voltage is in an unstable state, the data transfer method that can be executed in that state is executed as much as possible, and the transmission for transmitting data is performed. It is an object of the present invention to provide a data transfer method and a data transfer system that are safe not only for the means but also for the receiving host terminal that receives data.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a data transfer method for transferring data from a transmission means to a receiving host terminal through a communication line, a step of checking the value of the power supply voltage of the transmission means, A step of assigning an identifier corresponding to the value to predetermined unit data, a step of transferring the unit data to the receiving host terminal, a step of identifying the identifier assigned to the unit data by the receiving host terminal, and a result of the identification And a step of returning from the receiving host terminal a command for changing the transfer mode of the transmitting means according to the method.
[0008]
According to the present invention, by repeating the above steps, the receiving host terminal can detect a drop in the power supply voltage of the transmitting means and change the transmission mode of the transmitting means. Safe data transfer is also realized for the host terminal.
[0009]
The “transmission means” in the present invention means means having at least a transmission function, and need not be an apparatus specialized for the transmission function or an apparatus having a transmission function as a main function.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of a data transfer method and a data transfer system according to the present invention will be described in detail with reference to the accompanying drawings. In the figure, elements not directly related to the present invention are omitted, and similar elements are denoted by the same reference numerals. Further, the signal is represented by the sign of the signal line on which it appears.
[0011]
FIG. 1 is an overall block diagram of a data transfer system according to the present invention. The data transfer system 10 is a system for transferring image data from a digital camera 12 as a transmission means to a host PC (Personal Computer) 22 as a receiver. A memory card 14 for recording captured image data is detachable from the camera 12. The image data recorded on the memory card 14 is transferred to the public telephone network 18 through a communication line 16 such as ISDN (Integrated Services Digital Network), analog wired or wireless, and further provided with a communication device 20 such as a modem or a terminal adapter. To the host PC 22.
[0012]
However, these communication paths are merely examples. For example, image data may be transferred via a dedicated line or via the Internet, any communication line may be used, and either a wired or wireless line may be used. Although not shown, the present invention can also be applied to a configuration in which the camera 12 and the host PC 22 are directly connected to transfer image data. In that case, connection is possible by a connection cable such as a serial cable, a USB (Universal Serial Bus) cable, an IEEE (Institut of Electrical and Electronics Engineers) 1394, or a PC card slot.
[0013]
In the case of direct connection, it is particularly preferable to connect both 12 and 22 with a USB standard cable. If the camera 12 is compatible with the USB mass storage class (USB mass storage class), the memory card 14 of the camera 12 can be handled as a removable disk simply by connecting the two via a USB cable. Note that when the USB standard is used, the data transfer speed is fixed, and therefore, measures against a drop in the power supply voltage may be limited to measures for changing the data size or stopping the transfer.
[0014]
FIG. 2 is a block diagram showing the configuration of the digital camera 12. Although the camera 12 is an imaging device, in this embodiment, the camera 12 serves as a transmission unit that transfers image data that has been shot and recorded on the memory card 14 to the host PC 22 via the communication line 16.
[0015]
The camera 12 includes an image control unit 24 that mainly functions to transfer image data to the host PC 22. The image data photographed by the camera 12 is recorded on the memory card 14 by the memory card control unit 28 via the signal line 26, and is also taken out from the memory card 14 by the control unit 28 when transferring the image data.
[0016]
On the other hand, an electrically erasable PROM (Electrically Erasable Programmable Read Only Memory; EEPROM) 36 is a nonvolatile memory that can be freely written and read, and will be described later in detail, but cannot be transferred when image data transfer is interrupted. This is a memory for temporarily storing and protecting the data 35.
[0017]
The image control unit 24 checks the voltage value 32 of the power supply 30 as an important function according to the present invention in addition to the above-described image data transfer. Then, a packet 60, which is predetermined unit image data for transfer, is created from the image data 26, and a flag 64 is assigned to the packet 60 as an identifier corresponding to the confirmed power supply voltage value 32.
[0018]
The camera 12 also includes a communication line control unit 34 as means for transferring the data packet 60 to the host PC 22 and receiving the command packet 80 from the host PC 22. The control unit 34 connected to the image control unit 24 by the signal line 27 is connected to the communication line 16 and transfers the packet 60 through the line 16 at a predetermined transfer rate.
[0019]
The power supply 30 is connected to the line control unit 34, the memory card control unit 28, and the EEPROM 36 via switches SW1, SW2, and SW3, respectively. These switches SW1, SW2, SW3 are all opened and closed by switching means 29, 31, 33 of the image control unit 24. Therefore, the power supply 30 supplies power 32 to the elements 34, 28, and 36 by the switch operation of the image control unit 24.
[0020]
The clock control unit 38 is a device that returns a predetermined clock pulse 42 in response to a clock switching signal 40 from the image control unit 24. The image control unit 24 transfers the packet 60 at a transfer rate according to the clock pulse 42.
[0021]
In addition, the camera 12 includes a liquid crystal display (LCD) display unit 44, a key input unit 46, and a power switch 48. The image control unit 24 is supplied with power from the power supply 30 by the ON signal 52 of the power switch 48. In addition, the clock control unit 38 is controlled to oscillate the clock by the photographing instruction 54 and the image data transfer instruction interrupt 50 from the key input unit 46, and the LCD display unit 44 is turned on through the signal line 45.
[0022]
The operation when the image data transfer instruction 50 is applied from the key input unit 46 will be described. The image control unit 24 closes the switches SW2 and SW3 to supply power to the elements 28 and 36, and the clock control unit 38 is switched on. Control to switch the transfer speed by clock pulse to high-speed clock for transfer. In this way, the camera 12 can transfer a moving image to the host PC 22 while photographing. Next, the image control unit 24 reads the image data stored in the memory card 14 via the memory card control unit 28 and detects whether there is image data to be transmitted. SW1 is closed and the communication line control unit 34 is energized to transfer image data. At this time, as described above, the data is divided into unit image data called packets 60, and a predetermined flag 64 is assigned to each packet for transfer.
[0023]
In this embodiment, moving image transfer is handled, but it goes without saying that still images can also be transferred.
[0024]
FIG. 3 is a configuration diagram of an image data packet created by the image control unit 24. The packet 60 is composed of a packet ID 62 for distinguishing individual packets, a voltage flag 64 determined according to the voltage of the power supply 30, an image data portion 66, and a check sum 68 representing a packet length and the like. Yes. The flag 64 may be provided by providing an area of about 1 to 2 bits in the packet 60. This packet configuration is an example, and for example, a thumbnail image portion may be included. Also, the packet length is variable, and a method of transferring only thumbnail images according to the state of the power supply voltage can be adopted as will be described later.
[0025]
FIG. 4 is a diagram for explaining the state of the voltage flag 64 assigned to the packet 60 shown in FIG. According to FIG. 4, each flag 64 is 3 if the value of the power supply voltage is 2/3 or more of the normal value, 2 when the value is lowered to 1/3 to 2/3 of the normal value, and 1 of the normal value. It is 1 when it falls to / 5 to 1/3, and 0 when it falls to 1/5 or less of the normal value. However, this flag determination method is an example, and the types of flags are not limited to four. The flag 64 may be determined by dividing the power supply voltage into a plurality of stages at an arbitrary boundary value. For example, a method of changing the flag when the power supply voltage with a normal value of 1.5 V drops to 1.25 V may be employed. As will be described later, the data transfer rate is changed according to the values of these flags 64 as shown in FIG.
[0026]
FIG. 5 is a block diagram showing the configuration of the host PC 22. The host PC 22 is a device that activates predetermined application software 92 to receive image data from the camera 12. The host PC 22 includes a communication line control unit 70, which is a device that receives the transfer of the packet 60 via the communication device 20. A CPU (Central Processing Unit) 72 is an element that plays the most important role in the present embodiment, and is a device that controls all operations of the host PC 22. The CPU 72 mainly receives the image data 74 received in the format of the packet 60, identifies the voltage flag 64 given to the packet 60, and determines the transfer mode of the camera 12 according to the identification result of the flag 64. Is a device that sends back a command to change. As a result, the host PC 22 on the receiving side can detect a drop in the power supply voltage of the camera 12 and change the transfer mode of the camera 12.
[0027]
The above-described command for changing the transfer mode of the camera 12 includes changing the data transfer speed of the camera 12 and stopping the data transfer from the camera 12.
[0028]
The CPU 72 sends back a command to lower the data transfer speed according to the degree of the power supply voltage drop of the camera 12, and sends back a command to stop data transfer when the power supply voltage falls below a predetermined value. Specifically, as shown in FIG. 4, the data transfer rate is changed according to the value of the identified voltage flag. In the figure, when the value of the flag 64 is 3, the normal transfer rate of 30 frames / second is maintained. On the other hand, when the value of the flag 64 is 2, the data transfer rate is reduced to 10 frames / second, and when the value of the flag 64 is 0 or 1, the transfer rate is set to 0 frame / second. That is, the data transfer is stopped.
[0029]
These transfer speeds are also exemplary, and a method of reducing 30 frames / second to a speed of 15 frames / second, 8 frames / second, or the like may be employed. Further, it may be possible to cope with the voltage drop by changing the size of the packet itself, not the transfer speed, or by transferring only the thumbnail image with a small data amount without transferring the entire image data. .
[0030]
FIG. 6 is a configuration diagram of an instruction packet for realizing such a transfer mode switching instruction. The instruction packet 80 is created by the CPU 72 that has identified the flag 64 of the data packet 60, and includes a packet ID 82, an instruction command portion 84, and a check sum 86, as shown in FIG. Various instructions corresponding to the flag 64 are described in the instruction command section 84.
[0031]
Please refer to FIG. 5 again. The host PC 22 further includes a memory 94 that stores the received image data 90 and application software 92 that is activated when the image data is received. The CPU 72 reads and activates the application 92 from the memory 94 and identifies the flag 64 of the image data packet 60. At this time, even if the flag 64 has a value of 0 to 2 and it is necessary to issue a command to reduce the transfer speed, it may be an obstacle to the operation of the application 92. This is because some applications require that the transfer rate of received data be maintained at a predetermined value or higher. Therefore, even if the data transfer can be continued if the transfer rate is lowered, the data transfer is interrupted if the application 92 requests it. As a result, the occurrence of an abnormality in the host PC 22 is prevented.
[0032]
Compared with the case where the transmission means (corresponding to the camera 12 in this embodiment) used in the prior art unilaterally interrupts the data transfer, the feature of the present invention is only permitted by the application 92. For example, the present invention has an advantage that data transfer can be continued at a low transfer rate. Therefore, an abnormality of the host PC 22 due to a sudden interruption of data transfer is avoided.
[0033]
Thus, the present invention is characterized in that the host PC 22 that receives data has the authority to determine the transfer mode of the transmission means. Thereby, the situation of the host PC 22 is considered to the maximum. That is, an instruction to change the transfer mode of the camera 12 can be returned from the host PC 22 within a range allowed by the application 92 executed on the host PC 22. As a result, safe data transfer is executed without causing any inconvenience not only in the camera 12 but also in the host PC 22.
[0034]
Next, the operation of the embodiment of the present invention configured as described above will be described with reference to FIGS. FIG. 7 is a flowchart showing the operation of the camera 12, and FIG. 8 is a flowchart showing the operation of the host PC 22. FIG. 9 is a schematic diagram showing signals traveling between the camera 12 and the host PC 22 in time series.
[0035]
First, when the power switch 48 of the camera 12 is turned on, the flowchart of FIG. 7 is started. The image control unit 24 receives power supply from the power supply 30 and is activated. As a result, the control unit 24 can open and close the switches SW1, SW2, and SW3. Next, in response to a shooting instruction 54 from the key input unit, the image control unit 24 operates an optical system (not shown) to start shooting, closes SW2, and records the shot image on the memory card 14.
[0036]
When there is a moving image transfer instruction interrupt 50 from the key input unit 46, the data transfer operation step S100 of FIG. 7 is started. Note that step 100 may be started in response to a transfer request from the host PC 22. The image control unit 24 oscillates the clock control unit 38 and starts supplying the clock pulse 42, while turning on the LCD display unit 44. Further, the switch SW3 is closed to supply power to the EEPROM 36.
[0037]
The completion of the data transfer operation in this way is transmitted to the host PC 22 by a predetermined signal. Then, from the CPU 72 of the host PC 22, as shown in step S107 of FIG. 8 and FIG. 9, an instruction packet 80A for setting the data transfer rate to the normal 30 frames / second arrives as an initial condition. This is received by the camera 12 in step S101. Note that the instruction packets 80A to 80C appearing below are variations of the packet 80 described with reference to FIG. 6 and have the same configuration.
[0038]
Next, step S <b> 102 for confirming the voltage value 32 of the power supply 30 of the camera 12 as a transmission unit is executed by the image control unit 24. A voltage flag 64 as an identifier corresponding to the confirmed power supply voltage value 32 is given to predetermined unit data created from the image data, that is, the packet 60.
[0039]
It is assumed that the voltage value 32 is 2/3 or more of the normal voltage value. Then, according to FIG. 4 and as shown in FIG. 9, a packet 60A with the value of the flag 64 set to 3 is created and transferred in step S104. The data packets 60A to 60F that appear below are variations of the packet 60 described in FIG. 3, and have the same configuration. The packet transfer speed at the beginning of data transfer is 30 frames / second given as an initial condition by the packet 80A. The image control unit 24 controls the clock control unit 38 to obtain a high-speed clock pulse 42 so as to achieve a transfer rate of 30 frames / second, and performs data transfer.
[0040]
The CPU 72 of the host PC 22 always waits for a data packet in the packet waiting step S110. When the packet 60A is received here, the CPU 72 identifies whether or not the voltage flag 64 of the packet 60A has changed from the value 3 that is the initial condition in step S112. In this case, since the flag 64 has the value 3 as the initial condition, the process advances to step S114 to store the packet 60A as the image data 90 in the memory 94. Then, the process proceeds to step S106 of the camera 12, and the transfer of the data packet is continued until the transfer of all data is completed.
[0041]
While the data packet having the flag 64 value of 3 is transferred as in the packet 60A, the voltage value 32 is not abnormal, so that the packets 60A to 60B having a transfer rate of 30 frames / second according to the initial conditions are transferred. Continue to be. The packets 60A and 60B are representatively shown, and much more packet transfers are actually performed.
[0042]
However, if for some reason it is determined in step S102 that the power supply voltage has dropped from the normal voltage, it is difficult to continue image data transfer. In that case, the process proceeds to step S108, and according to FIG. 4 and as shown in FIG. 9, a packet 60C in which the value of the voltage flag 64 is 2 is created according to the degree of voltage drop. However, even if the voltage value 32 is so low that it is determined to be abnormal, the camera 12 does not have the authority to change the transfer rate. Accordingly, the transfer rate of the original packet 60C in which the flag is changed to 2 remains at 30 frames / second given as the initial condition by the packet 80A.
[0043]
In the host PC 22, when a data packet having a flag 64 value of 2, such as the packet 60C, is transferred, the flag value has changed to a value other than 3 in step S112, that is, the power supply voltage value of the camera 12 Detect that is abnormal. Accordingly, the process proceeds to step S118 where the packet 60C is stored in the memory 94 and the transfer mode switching command packet 80B of the camera 12 is transmitted to the camera 12. The command command 84 of the command packet 80B changes the data transfer rate to 10 frames / second in accordance with the flag value 2 according to FIG. 4 and as shown in FIG.
[0044]
When receiving the command packet 80B in step S120, the image control unit 24 of the camera 12 transmits an Acknowledge signal to the host PC 22 for confirming that the switching command has been received in step S122. This is received by the CPU 72 of the host PC 22 as shown in step S124. The switching of the transfer mode due to the power supply state failure may be notified to the user of the host PC 22 by some display device (not shown).
[0045]
On the other hand, as shown in step S126, the image control unit 24 of the camera 12 switches the transfer mode of the camera 12 in accordance with the command command 84 of the command packet 80B. Specifically, according to FIG. 4, the clock control unit 38 is controlled so as to change the data transfer rate according to the value of the flag 64 to obtain a predetermined clock pulse 42.
[0046]
In step S128, if the transfer mode after switching is a transfer speed change as described above, the process proceeds to step S106 to determine whether or not all data transfer is completed, and if not completed, the process returns to step S102 and ends. If so, the process ends.
[0047]
As typically shown in the packets 60D to 60E, if the degree of voltage drop is constant, the data packet transfer rate is maintained at 10 frames / second. However, when the power supply voltage of the camera 12 further decreases and the flag value 64 becomes 1, as shown in the packet 60F, the host PC 22 creates the transfer mode switching command packet 80C in step S118, and 12 to send. The instruction command 84 of the instruction packet 80C changes the data transfer rate to 0 frame / second in accordance with the flag value 1 in accordance with FIG. 4 and as shown in FIG. That is, the image transfer is stopped.
[0048]
In this case, in step S128, since the transfer mode after switching is the data transfer stop, the process ends. At that time, the power supply 30 may be turned off if necessary.
[0049]
When the data transfer rate is changed or the data transfer is stopped, the image control unit 24 temporarily saves the packet being transferred to the EEPROM 36 and protects the data until the normal state is restored. That's good. Further, the switching of the transfer mode due to such a power supply state failure is displayed on the LCD display unit 44 by the image control unit 24 and may be notified to the user.
[0050]
As described above, the feature of the data transfer method according to the present invention is that the host PC 22 on the receiving side detects a drop in the power supply voltage of the camera 12 by repeating the steps shown in FIGS. Is to change the mode. Since the host PC 22 on the data receiving side has authority to determine the transfer mode change of the camera 12, the CPU 72 of the host PC 22 can determine the transfer mode of the camera 12 in consideration of the image data receiving application 92. . Therefore, regardless of the value of the flag 64, the transfer mode of the camera 12 can be changed according to the request of the application 92.
[0051]
In this embodiment, the monitoring target is the power supply voltage of the camera 12, but the monitoring target is not limited to this. For example, as seen in the prior art, the remaining battery level may be detected, and the transfer mode may be changed based on this remaining battery level.
[0052]
As described above, the present invention has been described with the embodiment in which the transmission means is a digital camera and the receiving host terminal is a personal computer server. However, the present invention is not limited to cameras. For example, a notebook computer, a portable information terminal, a mobile phone, or a handy printer may be used as the transmission means.
[0053]
【The invention's effect】
As described above, according to the present invention, data transfer is stopped when a power failure occurs during data transfer, so that damage to a storage device such as a flash memory can be prevented. As a result, it is possible to eliminate data destruction and subsequent malfunctions. Here, the characteristic of the present invention is that, unlike the conventional technique that focuses on the remaining battery level, the data communication method is changed by focusing on the power supply voltage. Therefore, an error in data transfer that occurs only when the power supply voltage becomes unstable can be avoided without fear of running out of the battery.
[0054]
Further, according to the present invention, when the power supply becomes weak, it is not always necessary to stop the data transfer. Functions that do not drain the battery significantly enable processing. That is, the effect that data transfer can be continued at a low speed is obtained.
[0055]
Further, when the lowered power supply voltage is recovered, there is an advantage that the data transfer speed is increased again and efficient data transfer can be performed.
[0056]
Of particular note is that the present invention is characterized in that the receiving host terminal determines whether the transfer rate is reduced or the transfer is stopped, so that the transmission means transfer mode can be changed in consideration of the application of the receiving host terminal. That is. This realizes safe data transfer not only for the transmission means but also for the receiving host terminal.
[Brief description of the drawings]
FIG. 1 is an overall block diagram of a data transfer system according to the present invention.
FIG. 2 is a block diagram showing the configuration of the digital camera shown in FIG.
3 is a configuration diagram of an image data packet created by the image control unit shown in FIG. 2. FIG.
4 is a diagram for explaining a state of a voltage flag shown in FIG. 3. FIG.
5 is a configuration block diagram of the host PC shown in FIG. 1. FIG.
6 is a configuration diagram of an instruction packet created by the CPU shown in FIG. 5;
7 is a flowchart showing the operation of the digital camera shown in FIG.
FIG. 8 is a flowchart showing the operation of the host PC shown in FIG.
FIG. 9 is a schematic diagram showing signals traveling between the digital camera and the host PC shown in FIG. 1 in time series.
[Explanation of symbols]
10 Data transfer system
12 Digital camera
14 Memory card
22 Host PC
24 Image control unit
30 power supply
38 Clock controller
60 data packets
64 voltage flag
72 CPU
92 Application software

Claims (8)

In a data transfer method for transferring data from a transmission means to a receiving host terminal through a communication line, the method includes:
A step of confirming the value of the power supply voltage of the transmission means;
A step of assigning an identifier corresponding to the value of the confirmed power supply voltage to predetermined unit data;
Transferring the unit data to the receiving host terminal;
Identifying the identifier assigned to the unit data with the receiving host terminal;
Returning from the receiving host terminal an instruction to change the transfer mode of the transmitting means according to the identification result;
Transferring the data in the transfer mode in accordance with the command in the transmitting means. 2. The method according to claim 1, wherein the instruction to change the transfer mode of the transmission means includes an instruction to change the data transfer rate of the transmission means or to stop data transfer from the transmission means. Data transfer method. 3. The method according to claim 2, wherein the command reduces the data transfer speed in accordance with the degree of decrease in the power supply voltage of the transmission means, and stops data transfer when the power supply voltage becomes a predetermined value or less. A data transfer method characterized by the above. 2. The method according to claim 1, wherein in the step of replying from the receiving host terminal, a command for changing the transfer mode of the transmitting means is allowed within the range allowed by the application software executed on the receiving host terminal. A data transfer method characterized by sending a reply from a host terminal. In a data transfer system that includes a transmission means and a reception-side host terminal and transfers data through a communication line from the transmission means to the reception-side host terminal, the transmission means includes:
Means for confirming the value of the power supply voltage of the transmission means and giving an identifier corresponding to the confirmed power supply voltage value to predetermined unit data;
Means for transferring the unit data to a receiving host terminal, the receiving host terminal comprising:
Means for identifying an identifier given to the unit data and returning a command for changing the transfer mode of the transmission means according to the identification result;
Thus, a data transfer system characterized in that the receiving host terminal detects a drop in the power supply voltage of the transmission means and changes the transfer mode of the transmission means. 6. The data transfer system according to claim 5, wherein the instruction to change the transfer mode of the transmission unit includes a change of a data transfer rate of the transmission unit or a stop of data transfer from the transmission unit. system. 7. The system according to claim 6, wherein as a result of the identification, the means for returning the instruction returns an instruction for reducing the data transfer rate in accordance with the degree of decrease in the power supply voltage of the transmission means, and the power supply voltage is A data transfer system which returns a command to stop data transfer when a predetermined value or less is reached. 8. The data transfer system according to claim 5, wherein the communication line is a wired or wireless line.

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