JPH0574974B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bidirectional data communication method between one master device and a plurality of slave devices.

[Conventional technology]

Recently, in order to enjoy video information, video cameras such as VTRs, television tuner units,
Progress is being made in creating a system equipped with multiple peripheral devices such as a timer unit and an editing machine. In this case, the method of communication of control data such as mode signals and various control signals between the VTR and each peripheral device becomes a problem, but if the method of communication of this control data is unified in this system, it will be common. It is possible to achieve generalization, generalization, and low cost.

One conceivable method for this communication is to use the VTR as a master device and use multiple peripheral devices as slave devices to perform bidirectional communication. In this case, there is a need to reduce the number of communication lines as much as possible. This is especially true when there are a large number of slave devices.

Therefore, from the perspective of the master device, a method using only two communication lines, a transmission communication line and a reception communication line, or a method in which bidirectional communication can be performed using only one communication line may be considered.

As one of these methods, the applicant has already proposed a method in which bidirectional communication can be performed using only one communication line (see international application PCT/JP84/00425).

In other words, in this method, a communication section consisting of a plurality of time-divisionally provided transmission areas for master devices and transmission areas for slave devices is considered as one block, and this is repeated periodically. This method is performed only by the master device. In this case, transmission areas for slave devices are provided as many as the number of slave devices.

Even when two transmission lines, one for the master device and one for the slave device, are used, there is only one transmission line from the slave device's perspective, so when performing periodic communication as described above, the transmission from each slave device is must be carried out in transmission areas provided on a time-division basis.

[Problem that the invention seeks to solve]

However, when a time-division transmission area is provided for all of a plurality of slave devices, there is a drawback that when the number of slave devices increases, the transmission cycle of each slave device becomes extremely long.

In addition, since each slave device does not always send a request for transmission to the master device, if a transmission area is set up for all multiple slave devices as described above, there will be a transmission area that is not used or does not need to be used, and is used inefficiently.

[Means for solving problems]

In this invention, for example, as shown in FIGS. 1 to 4, when serial data is bidirectionally communicated between a master device 10 and a plurality of slave devices 20 via a communication line 30, time A communication section consisting of a plurality of communication areas that do not overlap each other is periodically repeated, and each of the plurality of communication areas is assigned to either the transmission area of the master device 10 or the transmission area of the slave device 20.
In a data communication method in which both areas can be identified and the number of transmission areas of the slave device 20 is smaller than the number of the plurality of slave devices 20, the master device 10 manages communication time. In the device 20,
The first step is to compare bit by bit the data sent from the slave device 20 to the communication line 30 in the predetermined communication area _P1 and the data actually transmitted over the communication line 30 (step S102 in FIG. 1). When a difference between the data sent to the communication line 30 and the data actually transmitted via the communication line 30 is detected (step S103; YSE in FIG. 1), the slave device 2
0 to the communication line 30, and the above-mentioned first and second steps are repeated in the communication area _P2 next to the predetermined communication area _P1 . .

[Effect]

The transmission area of each slave device is not specified, but a slave device with a transmission request selects any vacant transmission area and performs transmission in that transmission area. Therefore, even if transmission requests from slave devices collide, the transmission areas are switched, and the master device can reliably receive the transmission data from all slave devices that have transmission requests.

〔Example〕

FIG. 4 shows an embodiment of a communication system to which the method of the present invention is applied, in which serial data can be communicated bidirectionally through a single communication line. Also, in this example, the master device
This is an example where three or more VTRs and slave devices are provided, such as a video camera, a TV tuner unit, an editing machine, etc., and the configuration of the communication control section on the slave side is the same, so only the video camera is shown in the example in the figure. be.

That is, in the figure, 10 is a VTR, and 20 is a video camera.

Further, 30 is one data communication line for transmitting control data between the VTR 10 and the video camera 20 and other slave devices.

The VTR 10 includes a control section 11 equipped with a microcomputer (hereinafter referred to as microcomputer) 110 for controlling communication and other functions, a video circuit and mechanical deck section 12, and a function key section 13 of the VTR.
It consists of a VTR mode display section 14, a function key section 15 for remote control of the camera 20 (hereinafter referred to as remote control), and the like.

The video camera 20 also includes a control unit 21 equipped with a microcomputer 210 and configured to perform communication and other controls;
Camera function key section 22 and VTR 1
0 remote control function key section 23;
For example, it has a display section 24 that can be displayed within the viewfinder. Furthermore, motors 25F and 25Z that rotate the focus ring and zoom ring of the imaging lens, respectively, and an iris motor 25I that controls the opening/closing degree of the aperture are connected to the control unit 21 via motor drive circuits 26F, 26Z, and 26I. .

The function key section 13 of the VTR 10 is recorded,
It has function keys such as play, pause, fast forward, rewind, and stop, and when any of these keys is operated, the microcomputer 110 of the control unit 11 identifies it and displays it on the display unit 14. At the same time, necessary control signals are supplied to the video circuit and mechanical deck unit 12, so that the VTR is placed in a mode corresponding to the operated key.

The remote control function key unit 23 of the VTR 10 on the video camera 20 side also has function keys such as record, play, pause, fast forward, rewind, and stop. , connect the communication line 30 from the camera 20 side.
Control data is sent to VTER10 through
This is taken into the register of the microcomputer 110 of the control unit 11, and the contents of the data and the current
The mode of the VTR 10 is determined based on the key input state of the function key section 13 of the VTR 10,
The mode is displayed on the display section 14, and necessary control signals are supplied to the video circuit and mechanical deck section 12, so that the mode is set. The VTR 10 receives data sent from the camera 20 and the status of the function key section 13 of the VTR 10.
The reason for determining the mode is to prevent erroneous operation. For example, since there is usually no fast-forward mode during camera recording, in this case, the fast-forward command is ignored and the recording state continues. This is done by having the microcomputer 110 memorize which mode the VTR 10 should be placed in next based on the combination of remote control signals and function key modes.

Further, the VTR 10 sends back signal data indicating that it has entered the mode to the camera 20 side, and the camera 20 side receives it and displays the mode of the VTR 10 on the display section 24 in the viewfinder.

Further, the remote control function key unit 15 of the camera 20 of the VTR 10 has keys such as focus, iris, zoom, pan, and tail.
Sent from VTR 10 to camera 20, camera 2
The zooming data is taken into the register of the microcomputer 210 of the control unit 21 of No. 0, and is supplied to the zoom motor 25Z through the motor drive circuit 26Z to perform a zooming operation.

Function key part 22 in camera 20
When a key operation is performed, an operation corresponding to the key operation is performed in the camera 20 by a signal from the microcomputer 210 of the control section 21. For example, if a zoom key is operated on the camera 20, a zooming operation will be performed.

Control unit 11 of VTR 10 and video camera 20
The control section 21 is configured as follows. Control unit 2
1 has exactly the same configuration in other slave devices.

Microcomputer 110 of control unit 11 of VTR 10 and microcomputer 210 of control unit 21 of video camera 20
has 8-bit shift registers 111 and 211.
The shift registers 111 and 211 each have a serial input terminal SI, a serial output terminal SO, and a clock terminal CK. In addition, these shift registers 111 and 21
1 is designed to be written and read in the form of parallel data between it and the data bus of the microcomputer.

Furthermore, the loading of serial data into the shift registers 111 and 211 and the reading of serial data are controlled by communication controllers 112 and 212, respectively. These communication controllers 112 and 212 control input gate switches 113 of shift registers 111 and 211, respectively.
and 213 and output gate switches 114 and 21
4, G ₁ , G ₂ and G ₁ ′,
G ₂ ′ and shift clocks CLK and CLK for shift registers 111 and 211.
CLK' (one cycle is, for example, 104 μsec).

Further, the communication controller 112 on the side of the VTR 10 serving as a master device generates a star bit based on the communication start signal CS from the microcomputer 110. The communication controller 212 on the video camera 20 side of the slave device does not generate a start bit. That is, communication time management is performed only by the VTR 10, which is the master device.

These communication controllers 112 and 212 can also be realized by microcomputers.

115 and 215 are input transistors, 116
and 216 are output transistors; the collectors of the output transistors 116 and 216 are connected to the power supply terminal via resistors 117 and 217, the collectors are connected to the communication line 30, and the emitters are grounded. In addition, the shift register 11 is connected to the bases of the output transistors 116 and 216 via output switches 114 and 214.
Serial data from 1 and 211 is supplied.

Furthermore, communication line 30 is connected to input transistors 115 and 21 via resistors 118 and 218, respectively.
5 base. The emitters of these transistors 115 and 215 are grounded, and the collectors are connected to the power supply terminal via resistors 119 and 219, and the collectors are connected to the shift register 11 via input switches 113 and 213.
1 and 211 serial input terminals.

Therefore, when no data is transmitted through the communication line 30, it is connected to the voltage of the power supply terminal (+5V) via the resistors 117 and 217.
It is always at a high level of +5V.

In the above configuration, bidirectional communication between the VTR 10 as the master device and the video camera 20 as the slave device is performed by the third device in this example.
As shown in the figure, this is done in vertical cycles in synchronization with the vertical synchronization signal VD.

In other words, from the perspective of the master device VTR10,
A section consisting of four areas: reception areas (slave device transmission areas) P ₁ and P ₂ and transmission areas P ₃ and P ₄ is defined as one communication section, and this and a certain period of rest section are used as vertical synchronization signal VD. Synchronize and repeat in a vertical period. In this case, there are two slave device transmission areas, _P1 and _P2 , which are smaller than the number of slave devices. Transmission from the slave device is performed using the vacant area of areas _P1 and _P2 , as will be described later.

The first bit of each area P ₁ , P ₂ , P ₃ , P ₄ is used as a start bit, which is obtained only from the VTR 10 as the master device, and based on this, transmission and reception between the master device and slave devices is performed. will be done. That is, the communication controller 112 sends four start bits for one communication section.
SB is made to occur repeatedly at a constant period.

Furthermore, 8-bit serial data _D0 to _D7 are transmitted in each of the transmission areas _P1 to _P4 ,
These 8-bit data _D0 to _D7 constitute one word. In this case, since there are four communication areas in one communication section, four words of data are exchanged within one vertical period TF. In this way, the number of words and bits within the communication interval are fixed, so
The length of the communication section is constant. Therefore, the length of the pause section is also constant.

Transmission and reception within one communication section is performed as follows. First, transmission from the master device will be explained.

A communication start signal CS (FIG. 5A) is generated from the microcomputer 110 of the master device, and is supplied to the communication controller 112. This communication start signal CS is normally "1" and falls to "0" when it is requested to start communication. In this example, it falls four times in one vertical period TF. Communication controller 1
When this communication start request is made in 12, for example, a start bit SB (FIG. 5B) which is "1" for a period of 1 bit with a specified length of 104 μsec from the falling edge of the signal CS is obtained, and this is the output transistor 11.
6, and is supplied to the communication line 30 to which the collector is connected as a "0" signal with inverted polarity.

Further, following this start bit SB, eight clock pulses CLK (FIG. 5C) with a clock period of 104 μsec are obtained from the communication controller 112, and these are supplied to the clock terminal of the shift register 111. Also, the control signal G ₁ (FIG. 5D) of the output switch 114 is synchronized with these eight clock pulses.
The period of CLK becomes "1", and the output switch 114
turns on. In the microcomputer 110, the transmission data DT ₁ (FIG. 5F) is preset in the shift register 111, so these eight clock pulses CLK are used to control the shift register 111.
The 8-bit transmission data DT ₁ is read out from the output switch 114 and the output transistor 1.
16 to the communication line 30. Figure 5G
is the state of the signal on this communication line 30.

When this 8-bit transmission data _DT1 is sent out, the switch 114 is turned off, and therefore the communication line 30 is pulled up to "1". This "1" period continues for 2.5 to 5 bits. This 2.5~5
The period of the bit is the end bit (see Figures 3 and 5G). Normally, the end bit is about 2 bits, but in this example, all the processing is done by the microcontroller's software, so the stop bit is longer than normal, and the communication data is taken into another RAM of the microcontroller and stored. We have secured enough processing time to do this.

In this way, the transmission data transmitted from the master side in this transmission area is supplied to the base of the input transistor 215 of the slave device, for example, the video camera 20 side. And Starbit SB
At this point, this input transistor 215 is turned off, and its collector output rises to "1".
Then, this is detected by the communication controller 212, and the control signal G ₁ ' (fifth
Figure I) becomes "1" and 8 cycles
A clock pulse CLK' (FIG. 5K) of 104 μsec is obtained, and the switch 213 is turned on and the clock pulse CLK' is supplied to the clock terminal of the shift register 211. Therefore, VTR10
The transmission data DT ₁ from DT1 is transferred to this shift register 21.
1. Then, the captured data is transferred to the microcomputer 2 during the stop bit period.
At the same time, data DT ₂ to be transferred from the video camera 20 to the VTR 10 is set in the shift register 211.

At this time, data is also sent to other slave devices at the same time.
DT ₁ is imported, but whether or not to use the data DT ₁ in that slave device is determined by reading its contents in each microcomputer.

Next, the reception area when viewed from the master side, that is, the transmission of the slave device will be explained.

Now, when there is a transmission request from the video camera 20 and a transmission request signal DM is supplied to the communication controller 212, the video camera 20 enters a transmission standby state, and the shift register 211 stores transmission data DT ₂
(right side of FIG. 5H) is stored.

In this state, VTR1 is first placed in area _P1 .
Start bit from communication controller 112 of
SB is generated and transmitted to the video camera 20 via the transistor 116 on the communication line 30. Then, as shown on the right side of FIG. 5G, the data on the communication line 30 becomes "0" for one bit period. Therefore, the input transistor 215 of the video camera 20 is turned off, and its collector output becomes "1". The communication controller 212 detects this and sends a control signal to the output switch 214.
Since G ₂ ' (FIG. 5 J) becomes "1", this output switch 214 is turned on, and eight clock pulses CLK' are generated during the "1" period of this signal G ₂ '. It is supplied to the clock terminal of shift register 211. Therefore, data DT ₂
is read out from this shift register 211 (see FIG. 5H) and supplied to the communication line 30 via the output transistor 216.

On the other hand, the communication controller 112 on the VTR 10 side
After outputting the start bit SB, the control signal G ₂ (E in Figure 5) of the input switch 113 becomes "1".
As a result, this input switch 113 is turned on, and eight clock pulses CLK (Fig. 5C) are activated.
is obtained during the period in which the signal _G2 is "1".

Therefore, the data DT ₂ transmitted from the video camera 20 is supplied to the shift register 111 via the input transistor 115 and the switch 113, and taken into the shift register 111 by the clock pulse CLK.

Then, during the end bit period of this transmission area _P1 , it is transferred to the RAM of the microcomputer 110 and stored.

The above is a case where the first area P ₁ of the communication section is not used as a transmission area for other slave devices, but when this area P ₁ is also used as a transmission area for other slave devices, the following occurs. In this way, area collision is avoided and the transmission area of one slave device is switched to the next area _P2 .

FIG. 1 is a flowchart for this purpose, and a program according to this flowchart is executed by a microcomputer in a control section of each slave device.

That is, when a start bit is transmitted from the master device to each slave device at the beginning of area _P1 , the slave device requesting transmission sends the transmission data to the communication line 30 as described above (step [101]). ). At this time, the data sent to the communication line 30 and the status of the communication line 30 are checked bit by bit (step [102]). That is, if the sent data is "0", the communication line 30 connects to the output transistor 21.
6 is off, so the voltage is 5V, and if the data is "1", the output transistor 216 is turned on, so the voltage should be 0V.

However, when transmission data is being sent from multiple slave devices, when the data bit from one of the slave devices becomes "1", its output transistor 216 is turned on, so the data of the other slave devices is affected. It drops to 0V regardless of the voltage.
Therefore, the bit of the sent data is "0".
However, by detecting that the communication line 30 has become 0V, a difference between the sent data and the data transmitted via the communication line 30 is detected (step [103]). And this means that at the same time,
In this area _P1 , transmission from other slave devices is detected. As can be seen from the above, when a collision occurs where two or more slave devices transmit in the same transmission area, the transmitted data bits D ₀ to _{D 7}
The slave device that is in a state of transmitting "1" first is given priority, and that area is taken as the transmission area of that slave device. Then, in the slave device where it is detected that the transmitted data differs from the data communicated on the communication line 30 for each bit, all subsequent bits are set to "0" and that area _P1 is designated as the transmission area. This prevents communication errors from occurring in the transmission data of a predetermined slave device.

In this way, in the slave device that could not transmit in area _P1 , transmission data is sent out again by the start bit SB that arrives at the beginning of area _P2 (step [104]). and,
Whether this area _P2 is vacant or not is checked bit by bit in steps [105] and [106] in the same manner as described above, and if it is vacant, this area _P2 is selected as the transmission area of the slave device. . If it is not vacant, it is determined whether area P ₁ is vacant again in the next cycle,
Thereafter, the above operations are repeated until a vacant area is detected.

Figure 2 diagrammatically shows the above operation.
This example shows that a slave device (for example, a tuner) and a slave device (for example, an editing machine) have a transmission request that collides in area _P1 , and the slave device, the editing machine, has changed its transmission area to area _P2 .

Note that each bit is checked using shift register 2.
This can be easily achieved by changing the number of stages of 11 to 9 stages. Practically speaking, the currently used shift register built into a 4-bit microcomputer has nine stages, so it can be used as is.

In the idle section after the communication section consisting of areas _P1 to _P4 as described above, in the VTR 10, video camera 20, and other slave devices,
Processing is performed based on the content of the received data, and other tasks are also performed by time-sharing processing.

Thereafter, in the same way, the communication period in which one block consists of transmissions from the VTR 10 and transmissions from slave devices such as the camera 20 is repeated periodically with pause periods in between, and in this example, the start bit is the master device. Arising only from
Since the master device side manages the time, areas P ₁ to _{P 4} can be reliably determined, and communication sections and idle sections can be reliably distinguished.

As mentioned above, since communication is done periodically,
Even if there is a communication leak or a communication error, the correct content can be restored immediately.

In addition, in the above example, communication and other tasks can all be performed by a single chip microcontroller without using an expensive interface, so it is possible to perform bidirectional communication using a cheap consumer LSI and a single communication line. Digital data communication can be realized.

Furthermore, since communication is synchronized on the master device side, even if multiple tasks other than communication need to be processed in a time-sharing manner, there is no possibility that one task will stop midway through. will disappear.

Note that the generation of the start bit SB and the generation of clock pulses in the communication controller 112, as well as the detection of star bits and the generation of the clock pulses in the communication controller 212, may be controlled by a microcomputer, or may be controlled by a microcomputer as in the example shown in the figure. may be performed by providing separate hardware.

Furthermore, although the above example is a special example in which only one communication line is required, the present invention is also applicable to cases where two lines, a transmission line and a reception line, are provided between a master device and multiple slave devices from the perspective of the master device. Of course it is possible.

Further, although the above example checks whether the transmission area is empty or not, it is checked for each bit, it may of course be checked for each word (8 bits).

〔Effect of the invention〕

As described above, in this invention, transmission from a slave device is performed using any vacant area among a plurality of time division areas, so the number of time division areas may be less than the number of slave devices. , Also, there is less unused area,
Good usage efficiency. Further, when communication is performed at a fixed period, for example, a vertical period, the length of the communication section does not become unnecessarily long, and therefore, there is sufficient time for work other than communication to be performed during the pause period.

[Brief explanation of drawings]

Figure 1 is a flowchart for explaining this process, Figure 2 is a diagram schematically showing its operation, and Figure 3 is a flowchart for explaining this process.
FIG. 4 is a time chart for explaining the outline of the invention, FIG. 4 is a block diagram of an embodiment of a communication system implementing the invention, and FIG. 5 is a diagram for explaining the same. 10 is a VTR as a master device, 20 is a video camera as one of multiple slave devices,
P ₁ and P ₂ are transmission areas for slave devices, P ₃ and P ₄ are transmission areas for master devices, and 30 is a communication line.

Claims (1)

[Claims] 1. When serial data is bidirectionally communicated via a communication line between a master device and a plurality of slave devices, a communication section consisting of a plurality of communication areas that do not overlap in time is periodically communicated. Repeatedly, each of the plurality of communication areas is set to either the transmission area of the master device or the transmission area of the slave device, so that both areas can be identified, and the number of transmission areas of the slave device is the same as above. In a data communication method in which the number of slave devices is set to be smaller than the number of slave devices, and the master device manages communication time, the slave device transmits data from the slave device to the communication line in a predetermined communication area. a first step of comparing bit by bit between the data sent to the communication line and the data actually transmitted over the communication line; and when a difference between the data sent to the communication line and the data actually transmitted over the communication line is detected. , a second step of stopping the transmission of data from the slave device to the communication line; and repeating the first and second steps in the next communication area after the predetermined communication area. data communication method.