JP3603818B2 - Music data communication device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a multi-access LAN that enables effective transmission of MIDI data and the like.
[0002]
[Prior art]
As a LAN system using a multi-access bus, a CSMA (Carrier Sense Multiple Access) system is known. In this system, transmission is performed after confirming the presence / absence of a signal on a bus prior to data transmission by performing carrier sensing. As an improvement of the CSMA system, there is a CSMA / CD (CSMA with Collision Detection) system in which it is checked whether or not a collision has occurred during the transmission of a frame by the own station, and the transmission side determines whether transmission is correct or not. . A well-known CSMA / CD LAN is Ethernet. The carrier detection / collision detection scheme used in these schemes does not depend on the type of frame used, nor does it depend on the encoding scheme (if it is within a certain range of conditions).
[0003]
[Problems to be solved by the invention]
In such a bus-type LAN system, for example, when MIDI data is to be transmitted, it is necessary to store a MIDI message in a data portion of the frame according to a frame format used in the system and transmit the MIDI message. However, in this case, a gateway is made by software to reproduce the received data, and the transmission / reception adapter circuit becomes complicated and expensive. The present invention has been made in view of such circumstances, and has as its object to provide a multi-access LAN that can mix data of different protocols.
[0004]
[Means for Solving the Problems]
According to one aspect of the present invention, a music data communication device includes: a receiving unit that receives a data frame from a communication network in which a music data frame to which a preamble for determining a frame is added and another data frame are mixed; Output means for receiving only the music data frame, decoding the music data frame, and outputting music data for each frame.
[0005]
According to another aspect of the present invention, a music data communication apparatus receives a data frame from an Ethernet (registered trademark) network in which a MIDI data frame to which a preamble for determining a frame is added and another data frame are mixed. Receiving means for receiving only the MIDI data frame based on the preamble, decoding the MIDI data frame, and outputting music data for each frame.
[0006]
[Action]
By converting a continuous signal or an asynchronous signal into a frame and adding a preamble for discriminating the frame and transmitting the frame, data of completely different protocols (signal coding system / physical frame format) are mixed on the same bus. On the receiving side, based on the preamble, it is easy to receive only the music data frame and to combine it.
According to this method, the circuit configuration of the receiving adapter is very simple even when, for example, MIDI data is transmitted on the Ethernet. The transmission adapter also requires only high-speed processing for encoding / decoding and collision detection / retransmission control, and has a simple circuit configuration. Even when processing is performed in units of MIDI messages, this processing can be performed at a MIDI rate (320 μs per byte) and does not require high-speed processing.
[0007]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a main configuration of a bus type LAN according to an embodiment of the present invention. Here, general Ethernet is used as a protocol of the CSMA / CD system, and FIG. 1 shows a specific configuration of a transmission adapter and a reception adapter that transmit and receive MIDI data using the bus. As shown, a transmitting MIDI instrument 1 is connected via a MIDI cable 2 to a transceiver 4 on a bus via a transmitting adapter 3, and a receiving MIDI instrument 5 is connected via a MIDI cable 6 and a receiving adapter 7. It is connected to a transceiver 8 on the same bus.
[0008]
The transmission adapter 3 includes a serial / parallel converter 31 for converting MIDI data generated asynchronously from the MIDI musical instrument 1 into parallel data, and temporarily stores the converted data in a FIFO buffer 32 and then converts the converted data into serial data again. It has a serial converter 33, a modulator 34 for encoding the output of the converter 33 and sending it out to the bus, and a carrier sense / back-off control circuit 35. The serial / parallel converter 31 and the FIFO buffer 32 are provided to frame MIDI data in word units. The carrier sense / backoff control circuit 35 controls transmission start timing based on the reception signal and the collision detection signal obtained from the transceiver 4.
[0009]
The receiving adapter 7 is controlled by a demodulation circuit 71 for receiving and demodulating data transmitted on the bus transmitted via the MIDI musical instrument 1 and the transmitting adapter 3, a frame length counter 72, and the frame length counter 72. It has a gate circuit 73 that outputs data demodulated for each frame to the MIDI musical instrument 5.
[0010]
FIG. 2 shows a frame format used in this embodiment. FIG. 2A shows a general Ethernet frame format as a CSMA / CD protocol. The signal speed is 10 MHz, and the encoding method is biphase encoding (Manchester encoding) which is a phase modulation method. As shown in FIG. 2A, the bit pattern of the preamble PA is 31 10s followed by 1 11. DA / SA following the preamble PA is a destination / source address, and Length represents the length of data Data. At the end of the data Data, an error check code CRC is attached. This code CRC allows the receiving side to remove the abnormal frame.
[0011]
On the other hand, the MIDI data frame format exchanged between the MIDI musical instruments 1 and 5 is as shown in FIG. The bit pattern of the preamble PA is, as shown in FIG. 2 (b), 31 01s and a subsequent 00. Although the relationship with the preamble of a normal frame is obtained by simply inverting the sign, there is no problem in the operation as the preamble. After the preamble PA, a 31.25 Kbps 10-bit start-stop synchronization signal in which 8-bit data bits D0, D1,..., D7 are sandwiched between a start bit Start and a stop bit Stop of 1 bit at a time. Data (3200 bits on the bus) follows. One bit of the MIDI signal is 32 μs, and the same data is transmitted for 320 bits.
[0012]
The operation of transmitting MIDI data will now be described. A MIDI signal input from the MIDI musical instrument 1 from the MIDI / IN connector of the transmission adapter 3 is stored in the FIFO buffer 32 via the serial / parallel converter 31 in word units. The carrier sense / back-off control circuit 35 performs carrier sense, and in accordance with an instruction from the carrier sense / back-off control circuit 35, a signal for one word is taken out from the FIFO buffer 32, converted into serial data by the parallel / serial converter 33, and then modulated. , And transmitted with a preamble. If no collision is detected, one word of data is discarded from the FIFO buffer 32 according to an instruction from the carrier sense / backoff control circuit 35. If a collision is detected, it is backed off for an appropriate time by an instruction from the carrier sense / backoff control circuit 35, and is retransmitted.
[0013]
The reception adapter 7 processes only a frame having a MIDI frame preamble. That is, the demodulation circuit 71 synchronizes the phase of the biphase signal with the MIDI frame preamble, decodes the subsequent biphase signal, and outputs the signal from the MIDI / OUT connector. At this time, the frame length counter 72 detects the received frame length. For example, if the MIDI frame length is too short due to a collision or the like (that is, less than 320 μs), the gate circuit 73 is controlled to output the MIDI / OUT signal. The output signal is forcibly held at 0 until 320 μs. This prevents output of a signal that causes a framing error on the receiving side.
[0014]
If the f / 2f method (that is, 0 is a fundamental wave and 1 is a wave using twice the frequency) is used as the encoding method on the MIDI signal transmitting side, the preamble is more effectively used. Can be used for That is, in the case of the f / 2f method, it is not necessary to perform the phase alignment of the bit boundary at the end of the preamble. Therefore, a preamble of 000... 0001 is used for a CSMA frame, and 111. A preamble can be used. When such a preamble format is used, in a MIDI frame, the preamble is no longer distinguished from an idle period, and the receiving side of the MIDI frame may simply output the decoded 1 to MIDI / OUT without being aware of the preamble. Also, if the MIDI transmitting side delays the MIDI / IN signal and encodes and transmits the state of 1 before the start bit, the end result is that the preamble has been transmitted.
[0015]
In the embodiment, the case where the MIDI signal as the asynchronous signal is mixed with the CSMA frame of another station in a different frame format has been described. However, the present invention is not limited to this, and the present invention is not limited to this. Is also effective when transmitting the modulated signal.
[0016]
【The invention's effect】
As described above, according to the present invention, with the addition of a simple transmission / reception adapter, a multi-access type that can easily transmit data according to different protocols in a mixed manner, receive only desired data, and decode the data is easy. A LAN can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a MIDI data transmitting / receiving section of a LAN according to an embodiment of the present invention.
FIG. 2 is a diagram showing two frame formats of the embodiment.
[Explanation of symbols]
1, 5 MIDI instrument, 2, 6 MIDI cable, 3 transmission adapter, 4, 8 transceiver, 7 reception adapter, 31 serial / parallel converter, 32 FIFO buffer, 33 parallel / serial converter , 34: modulator, 35: carrier sense / back-off control circuit, 71: demodulation circuit, 72: frame length counter, 73: gate circuit.

Claims (2)

Receiving means for receiving a data frame from a communication network in which music data frames to which a preamble for determining a frame is added and other data frames are mixed;
Output means for receiving only the music data frame based on the preamble, decoding the music data frame, and outputting music data for each frame,
A music data communication device having: Receiving means for receiving a data frame from an Ethernet (registered trademark) network in which a MIDI data frame to which a preamble for determining a frame is added and other data frames are mixed;
An output unit that receives only the MIDI data frame based on the preamble, decodes the MIDI data frame, and outputs music data for each frame;
A music data communication device having:

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