Transmitting method, receiving method, and communication method for bi-directional bus system, and bi-directional bus system

A communication system using a bi-directional bus, comprises a plurality of devices (e.g., TV Image Receiver, Video Tape Recorder, etc. ) respectively including sub-devices (e.g., Monitor Image Receiver, TV tuner, Video Deck, etc.) adapted for executing the operation for a received control command. Each device comprises a transmit signal formation unit for forming a transmit signal having a frame structure consisting of an address field for specifying addresses of devices between which communication is carried out, and a data field for specifying a control command for a device or a sub-device, and including a channel select code of a fixed length, inserted at a predetermined position of the data field, indicating communication from a sub-device included in a device to any other device, communication from a device to a sub-device included in any other device, or communication from a device to a device; and a bus output unit for outputting, to the bi-directional bus, the transmit signal formed by the transmit signal formation unit.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a transmitting method, a receiving method, a 
communication method, and a bi-directional bus system, which are used in a 
system in which devices, e.g., a television image receiver or a video tape 
recorder, etc. are connected to each other by using a bi-directional bus 
to control, from other devices, sub-devices, e.g., a monitor image 
receiver, a TV tuner, or a video deck, etc. included in the devices. 
2. Description of the Related Art 
In recent years, there have been popularly used systems in which a 
plurality of audio equipments or visual equipments (hereinafter referred 
to as AV equipments) are connected by means of video signal lines or audio 
sinal lines (hereinafter referred to as AV signal lines). 
In such AV systems, equipments are connected by means of a system control 
bus (hereinafter simply referred to as a bi-directional bus) in addition 
to the above-described AV signal lines to control respective equipments. 
In a practical sense, Audio, Video and audiovisual systems Domestic 
Digital Bus (hereinafter referred to as D2B) standardized by the so-called 
publication 1030 of IEC, a Home Bus System (hereinafter referred to as 
HBS) standardized by the ET-2101 of EIAJ, and the like are known. Through 
the bi-directional bus, other devices are controlled from equipments 
(devices), e.g., a television image receiver, a video tape recorder, and a 
video deck player (hereinafter respectively referred to as TV, VTR, VDP), 
etc., or sub-devices, e.g., a monitor image receiver (TV monitor), a TV 
tuner, a video deck, or an amplifier, etc. included in other devices are 
controlled from devices. 
Namely, communication from a sub-device included in a device to a 
sub-device included in any other device (hereinafter referred to as 
communication from sub-device to sub-device), communication from a 
sub-device included in a device to any other device (hereinafter referred 
to communication from sub-device to device), communication from a device 
to a sub-device included in any other device (hereinafter communication 
from device to sub-device), and communication from a device to any other 
device are carried out through a bi-directional bus. In other words, 
communications are carried out through a plurality of routes (paths). 
The format of a transmit signal used in a bi-directional bus as described 
above, e.g., D2B will now be described. In D2B, control commands for 
controlling a sub-device of destination, etc. and/or data indicating the 
operating state, etc. are caused to have a frame configuration as shown in 
FIG. 1, and are transmitted through the bi-directional bus. 
Namely, one frame consists of a header field 101 for specifying the header 
indicating the leading portion of the frame, a master address field 102 
for specifying a source device address, a slave address field 103 for 
specifying a destination device address, a control field 104 for 
specifying control bits indicating communication, etc, in the state where 
a destination device is in a lock state, or in non-lock state, and a data 
field 105 for specifying control commands or data, 
The header of the header field 101 consists of, as shown in FIG. 2, a start 
bit 101a of one bit for providing synchronization, and mode bits 101b for 
prescribing a transmission speed (rate) or the number of bytes of the data 
field 106. These mode bits 101b are 1.about.3 bits. At present, three 
modes of mode 0 where the data field 105 is comprised of 2 bytes at the 
maximum, mode 1 where the data field 105 is comprised of 32 bytes at the 
maximum (16 bytes at the maximum in the case of communication from slave 
to master), and mode 2 where the data field 105 is comprised of 128 bytes 
at the maximum (64 bytes at the maximum in the case of communication from 
slave to master) are prescribed. 
The source device address of the master address field 102 consists of, as 
shown in the above-mentioned FIG. 2, master address bits 102a of 12 bits 
for specifying a source device address, and a parity bit 102b of 1 bit. 
The destination device address of the slave address field 103 consists of, 
as shown in the above-mentioned FIG. 2, a slave address bits 103a of 12 
bits for specifying a destination device address, a parity bit 103b of 1 
bit, and an acknowledge bit 103c of 1 bit for sending acknowledge from the 
destination device. 
The content of the control field 104 consists of, as shown in the 
above-mentioned FIG. 2, control bits 104a comprised of 4 bits indicating 
the direction of the control command, or indicating the lock state or the 
non-lock state, a parity bit 104b of 1 bit, and an acknowledge bit 104c of 
1 bit. 
In the data field 105, as shown in the above-mentioned FIG. 2, data bits 
105a of 8 bits, end of data bit 105b of 1 bit and parity bit 105c of 1 bit 
are repeated as occasion demands. Assuming now that data bits 105a are 
assumed to be data #1, #2, #3, . . . in order from the beginning, e.g., 
Operation code (hereinafter referred to as OPC) "Begin 2" (i.e., code 
"BD"h (h represents hexadecimal notation)) indicating communication 
relating to sub-device, OPC "Begin 1" ("BC" h) indicating communication 
through HBS, and OPC "Begin 0" ("BB"h) indicating communication through 
other bus, etc. are assigned (allocated) to data #1. Further, Operand 
(hereinafter referred to as OPR) with respect to these OPCs are assigned 
to data #2. 
OPR with respect to these OPCs, e.g., OPR with respect to OPC "begin 2" 
consists of, as shown in FIG. 3, bits b.sub.5, b.sub.4, b.sub.3, b.sub.2 
(b.sub.7 is the Most Signicant Bit (MSB) for identifying service codes of 
the Communication Telephony (CT) system, the Audio Video and Control 
(AV/C) system, and the Housekeeping (HK) system, etc.; and bits b.sub.1, 
b.sub.0 indicating any one of communication from sub-device to sub-device, 
communication from sub-device to device, communication from device to 
sub-device, and communication from device to device, viz., indicating 
presence or absence of Source Sub-Device Address (hereinafter referred to 
as SSDA) or Designation Sub-Device Address (hereinafter referred to as 
DSDA). It is to be noted that bit b.sub.7 is caused to be always zero, and 
bit b.sub.6 is reserved for future standardization and is caused to be 1 
at present. In more practical sense, b.sub.1 =0, b.sub.0 =0 indicates 
communication from sub-device to sub-device; b.sub.1 =0, b.sub.0 =1 
indicates communication from sub-device to device; b.sub.1 =1, b.sub.0 =0 
indicates communication from device to sub-device; and b.sub.1 =1, b.sub.0 
=1 indicates communication from device to device. 
Accordingly, e.g., in the communication from a sub-device of a TV (device) 
to a video deck (sub-device) of a VTR (other device), as shown in FIG. 4A, 
an address of TV is assigned as master address bits to the master address 
field 102; an address of VTR is assigned as slave address bits to the 
slave address field 103; and a code "A"h indicating write of a control 
command, e.g., from master to slave is assigned to the control field 104. 
Further, OPC "Begin 2" is assigned to data #1; e.g., code "54"h indicating 
communication from sub-device to sub-device is assigned to data #2 as OPR 
for OPC "Begin 2"; an address of a sub-device of TV is assigned to data #3 
as SSDA; and an address of a sub-device of VTR is assigned to data #4 as 
DSDA. To the subsequent data #5, e.g., control command for playing 
(reproducing) the video deck of VTR is assigned. 
Further, e.g., in the communication from sub-device of TV to VTR (device), 
as shown in 4B, address of TV, address of VTR and code "A"h indicating 
write of control command from master to slave are respectively assigned to 
the master address field 102.about.the control field 104, Further, OPC 
"Begin 2" is assigned to data #1, code "55"h indicating communication from 
sub-device to device is assigned to data #2, and address of sub-device of 
TV is assigned to data #3 as SSDA. Further, control command is assigned to 
data #4, Namely, in this case, since there is no destination sub-device, 
assignment of DSDA is unnecessary, 
Further, e.g., in the communication from TV (device) to sub-device of VTR, 
as shown in FIG. 4C, address of TV, address of VTR and code "A"h 
indicating write of control command from master to slave are respectively 
assigned to the master address field 102.about.the control field 104. 
Further, OPC "Begin 2" is assigned to data #1, code "56"h indicating 
communication from device to sub-device is assigned to data #2, and an 
address of sub-device of VTR is assigned to data #3 as DSDA. In addition, 
control command is assigned to data #4. Namely, in this case, since there 
is no source sub-device, assignment of SSDA is unnecessary. 
In addition, e.g., in the communication from TV (device) to VTR (device), 
as shown in FIG. 4D, address of TV, address of VTR, and code "A"h 
indicating write of the control command from master to slave are 
respectively assigned to the master field 102.about.the control field 104. 
Since there is no communication relating to the sub-device, control 
command is assigned to data #1. Namely, assignments of OPC "Begin 2", SSDA 
and DSDA are unnecessary. 
The control command will now be described. The number of codes that can be 
represented by 8 bits is 256. However, with 256 kinds of codes, it is not 
sufficient to carry out control of the entirety of the AV equipment. In 
view of this, in HBS or D2B, a command Table comprised of OPC and OPR 
shown in FIG. 5 is used. 
Namely, the command Table consists of OPC of 1 byte indicating the name of 
a controlled system, and OPR of 1 byte or plural bytes indicating the 
control content. General commands commonly used for respective equipments 
are assigned to code "AO"h.about.code "BF"h of OPC, a group of function 
commands are assigned to code "CO"h.about.code "DF"h, and a group of 
special function commands are assigned to code "EO"h.about.code "FF"h. In 
this case, code "80"h.about.code "9F"h are reserved. 
In more practical sense, control commands such as video commands, audio 
commands, deck/player commands or tuner commands, etc. share, e.g., the 
area of the function command group (code "CO"h.about.code "DF"h). For 
example, code "CO"h indicates control of contrast in the case of the video 
command, control of volume in the case of the audio command, repeat in the 
case of the deck/player command, and control of band in the case of the 
tuner command. 
Further, control commands such as video camera commands or timer commands, 
etc. share, e.g., the area of the special function command group (code 
"EO"h.about.code "FF"h). For example, code "EO"h indicates control of zoom 
in the video camera command, and year in the case of timer command. 
On the other hand, so called ASCTII code, controlling value code and alias 
code are assigned to code "20"h.about.code "5F"h of OPR, and standard OPR 
is assigned to code "60"h.about.code "7F"h. In this case, code 
"OO"h.about.code "1F"h are reserved. 
In more practical sense, e.g., standard OPR (code "60"h.about.code "7F"h) 
has common meanings every control commands such as video commands or audio 
commands described above. For example, code "60"h means ON, code "70"h 
means OFF, code "63"h means decrement, and code "73"h means increment. 
Meanwhile, in HBS, Table Selector (TS) (i.e., general command in which OPC 
consists of code "B9"h) is placed before the control command to prescribe 
correspondence relationship between OPC of the control command and the 
function command or the special function command. In D2B, command Table is 
selected in terms of default value by DSDA specified by OPC "Begin 2". In 
actual terms, e.g., in DSDA, video command is selected in TV monitor 
(sub-device), audio command is selected in audio amplifier, deck/player 
command is selected in video deck, video player, audio deck and CD player, 
and tuner command is selected in TV tuner and audio tuner. 
As described above, in the conventional communication method of D2B, etc., 
the position of OPC of the control command varies, e.g., in dependency 
upon the position of data #5, data #4, data #4, data #1 of data field 105 
and communication form (kinds of communication routes (paths)). Therefore, 
it is required for device or sub-device on the receiving side to specify 
the position of OPC prior to carrying out decode of OPC of the control 
command. For this reason, there was the problem that hardware or software 
becomes complicated. In addition, also in forming a transmit signal and 
transmitting such signal, the position of OPC of the control command 
varies depending upon communication route, resulting in the problem that 
software, etc. becomes complicated. 
OBJECT AND SUMMARY OF THE INVENTION 
In view of actual circumstances mentioned above, this invention has been 
made, and its object is to provide a transmitting method, a receiving 
method, a communication method, and a bi-directional bus system in which 
the position in the frame of the control command is fixed, thereby making 
it possible to simplify software, etc., e.g., for decoding control 
commands. 
To achieve the above-mentioned object, a first transmitting method 
according to this invention is directed to a transmitting method for a 
bi-directional bus system in which a plurality of devices respectively 
including sub-devices adapted to execute the operation with respect to a 
received control command are connected to each other through a 
bi-directional bus, wherein one frame of a transmit signal on the 
bi-directional bus consists of an address field for specifying addresses 
of devices between which communication is carried out and a data field for 
specifying a control command for device or sub-device, and a route select 
code of a fixed length indicating communication from a sub-device included 
in a device to any other device, communication from a device to a 
sub-device included in any other device, or communication from a device to 
any other device is inserted at a predetermined position of the data 
field, thus to transmit, through the bi-directional bus, a transmit signal 
in which the route select code is inserted. 
A second transmitting method according to this invention is characterized 
in that, in the first transmitting method, the route select code is caused 
to consist of a header operand indicating communication from a sub-device 
included in a device to any other device, communication from a device to a 
sub-device included in any other device, or communication from a device to 
any other device; and a sub-device address indicating a source sub-device 
address or a destination sub-device address, thus to allow the sub-device 
address to be dummy code in communication from the device to any other 
device. 
A first receiving method according to this invention is directed to a 
receiving method for a bi-directional bus system in which a plurality of 
devices respectively including sub-devices adapted to execute the 
operation with respect to a received control command are connected to each 
other through a bi-directional bus, characterized in that the receiving 
method comprises: receiving, through the bi-directional bus, a transmit 
signal having a frame structure consisting of an address field for 
specifying addresses of devices between which communication is carried out 
and a data field for specifying a control command for device or 
sub-device, and including a route select code of a fixed length, inserted 
at a predetermined position of the data field, indicating communication 
from a sub-device included in a device to any other device, a 
communication from a device to a sub-device included in any other device, 
or a communication from a device to any other device; detecting the route 
select code from the transmit signal; and detecting, on the basis of the 
detected route select code, whether a communication carried out is the 
communication from the sub-device included in the device to any other 
device, the communication from the device to the sub-device included in 
any other device, or the communication from the device to any other 
device. 
Further, a second receiving method according to this invention is 
characterized, in the first receiving method, in that the route select 
code consists of a header operand indicating a communication from a 
sub-device included in a device to any other device, a communication from 
a device to a sub-device included in any other device, or a communication 
from a device to any other device, and a sub-device address indicating a 
source sub-device address or a destination sub-device address, and that 
the receiving method comprises: detecting, on the basis of the header 
operand, whether a communication carried out is the communication from the 
sub-device included in the device to any other device, the communication 
from the device to the sub-device included in any other device, or the 
communication from the device to any other device; and specifying a source 
or destination sub-device on the basis of the sub-device address, and 
recognizing the sub-device address as a dummy code when the communication 
from the device to any other device is carried out. 
Further, a first communication method according to this invention is 
directed to a communication method for a bi-directional bus system in 
which a plurality of devices respectively including sub-devices adapted to 
execute the operation for a received control command are connected to each 
other through a bi-directional bus, characterized in that one frame of a 
transmit signal on the bi-directional bus is caused to consist of an 
address field for specifying addresses of devices between communication is 
carried out and a data field for specifying a control command for device 
or sub-device, that a route select code of a fixed length indicating a 
communication from a sub-device included in a device to any other device, 
a communication from a device to a sub-device included in any other 
device, or a communication from a device to any other device is inserted 
at a predetermined position of the data field, and that the communication 
method comprises: transmitting a transmit signal in which the route select 
code is inserted through the bi-directional bus; receiving the transmit 
signal through the bi-directional bus; detecting the route select code 
from the transmit signal; and detecting, on the basis of the detected 
route select code, whether a communication carried out is the 
communication from the sub-device included in the device to any other 
device, the communication from the device to the sub-device included in 
any other device, or the communication from the device to any other 
device. 
Further, a second communication method according to this invention is 
characterized, in the first communication method, that one frame of a 
transmit signal is caused to consist of a header field for specifying the 
header indicating the leading portion of the frame, a master address field 
for specifying a source device address, a slave address field for 
specifying a destination device address, a control field for specifying 
whether a data field is control command or data, and the data field 
comprised of a control command or data for device or sub-device, and that 
the route select code is inserted in the data field. 
A third communication method according to this invention is characterized, 
in the first communication method, in that a route select code is caused 
to consist of a header operand indicating a communication from a 
sub-device included in a device to any other device, a communication from 
a device to a sub-device included in any other device, or a communication 
from a device to any other device, and a sub-device address indicating a 
source sub-device address or a destination sub-device address, and that in 
transmission from a device to any other device, the sub-device address is 
transmitted as a dummy code, and in reception, whether a communication 
carried out is the communication from the sub-device included in the 
device to any other device, the communication from the device to the 
sub-device included in any other device, or the communication from the 
device to any other device is detected on the basis of the header operand 
to specify a source or destination sub-device on the basis of the 
sub-device address, and to recognize the sub-device address as a dummy 
code when the communication from the device to any other device is carried 
out. 
Further, a fourth communication method according to this invention is 
characterized, in the first communication method, in that a plurality of 
kinds of route select codes are prepared, that each route select code is 
caused to consist of a text header, a header operand indicating a 
communication from a sub-device included in a device to any other device, 
a communication from a device to a sub-device included in any other 
device, or a communication from a device to any other device, and a 
sub-device address indicating a source sub-device address or a destination 
sub-device address, and that the kind of the route select codes is 
indicated by the text header. 
A first bi-directional bus system according to this invention comprises a 
plurality of devices respectively including sub-devices adapted to execute 
the operation for a received control command; and a bi-directional bus, 
wherein each of the plurality of device transmit signal formation means 
for forming a transmit signal having a frame structure consisting of an 
address field for specifying addresses of devices between which 
communication is carried out, and a data field for specifying a control 
command for device or sub-device, and including a route select code of a 
fixed length, inserted at a predetermined position of the data field, 
indicating a communication from a sub-device included in a device to any 
other device, a communication from a device to a sub-device included in 
any other device, or a communication from a device to any other device to 
form a transmit signal; and bus output means for outputting the transmit 
signal formed by the transmit signal formation means to the bi-directional 
bus, the plurality of devices being connected to each other through the 
bi-directional bus. 
Further, a second bi-directional bus system according to this invention is 
characterized, in the first bi-directional bus system, in that each device 
includes user interface means for inputting operation contents, and the 
transmit signal formation means is operative to form a transmit signal in 
accordance with an operation content inputted from the user interface 
means. 
Further, a third bi-directional bus system according to this invention 
comprises a plurality of devices including sub-devices adapted to execute 
the operation for a received control means, and a bi-directional bus, 
wherein each of the plurality of devices comprises bus input means for 
receiving, through the bi-directional bus, a transmit signal having a 
frame structure consisting of an address field for specifying addresses of 
devices between which communication is carried out, and a data field for 
specifying a control command for device or sub-device, and including a 
route select code of a fixed length, inserted at a predetermined position 
of the data field, indicating a communication from a sub-device included 
in a device to any other device, a communication from a device to a 
sub-device included in any other device, or a communication from a device 
to any other device; and control means for detecting the route select code 
from the transmit signal received by the bus input means to detect on the 
basis of the detected route select code whether a communication carried 
out is the communication from the sub-device included in the device to any 
other device, the communication from the device to the sub-device included 
in any other device, or the communication from the device to any other 
device, the plurality of devices being connected to each other through the 
bi-directional bus. 
A fourth bi-directional bus system according to a fourth invention is 
characterized, in the third bi-directional bus system, wherein each 
sub-device has an input function or/and output function of an audio signal 
or/and video signal, and each device includes AV signal switching means 
for switching input/output destination of an inputted audio signal or/and 
video signal, and the control means is operative to control the AV signal 
selector means through internal communication means on the basis of 
control commands. 
A fifth bi-directional bus system according to this invention is 
characterized, in the third bi-directional bus system, in that each device 
further includes internal communication means for carrying out 
communication with a sub-device included in the device, the control means 
has a Table for converting a control command received by bus input means 
to an internal control command for controlling sub-device to convert the 
same control command to an internal control command of control contents 
corresponding to various controlled system sub-devices to transmit any 
internal command thus obtained to the sub-device through the internal 
communication means. 
A sixth bi-directional bus system according to this invention comprises a 
plurality of devices respectively including sub-devices adapted to execute 
the operation for a received control command, and a bi-directional bus, 
wherein each of the plurality of devices comprises transmit signal 
formation means for forming a transmit signal having a frame structure 
consisting of an address field for specifying respective addresses of 
devices between which communication is carried out, and a data field for 
specifying a control command for device or sub-device, and including a 
route select code of a fixed length, inserted at a predetermined position 
of the data field, indicating a communication from a sub-device included 
in a device to any other device, a communication from a device to a 
sub-device included in any other device, or a communication from a device 
to any other device, and indicating a source sub-device address, a 
destination sub-device address or a dummy code; bus output means for 
outputting the transmit signal formed by the transmit signal formation 
means to the bi-directional bus; bus input means for receiving the 
transmit signal through the bi-directional bus; and control means for 
detecting the route select code from the transmit signal received by the 
bus input means to detect, on the basis of the detected route select code, 
whether a communication carried out is the communication from the 
sub-device included in the device to any other device, the communication 
from the device to the sub-device included in any other device, or the 
communication from the device to any other device, and to specify a source 
sub-device, a destination sub-device or a dummy code, the plurality of 
devices being connected to each other though the bi-directional bus. 
In accordance with the first transmitting method according to this 
invention, a route select code of a fixed length indicating a 
communication from a sub-device included in a device to any other device, 
a communication from a device to a sub-device included in any other 
device, or a communication indicating a device to any other device is 
inserted at a predetermined position of data field of a transmit signal 
consisting of an address field and the data field to transmit, through the 
bi-directional bus, the transmit signal in which the route select code is 
inserted. 
Further, in accordance with the second transmitting method according to 
this invention, in communication from a device to any other device, a 
sub-device address of a route select code consisting of a header operand 
and a sub-device address is caused to be dummy code. 
Further, in accordance with the first receiving method according to this 
invention, a transmit signal consisting of address field and data field 
and including a route select code of a fixed length inserted at a 
predetermined position of the data field is received through the 
bi-directional bus to detect the route select code from the received 
transmit signal to detect on the detected route select code whether a 
communication carried out is communication from sub-device included in 
device to any other device, communication from device to sub-device 
included in any other device, or communication from device to any other 
device. 
Further, in accordance with the second receiving method according to this 
invention, whether a communication carried out is a communication from a 
sub-device included in a device to any other device, a communication from 
a device to a sub-device included in any other device, or a communication 
from a device to any other device is detected on the basis of header 
operand of a route select code consisting of the header operand and a 
sub-device address, and a source or destination sub-device is specified on 
the basis of the sub-device address to recognize the sub-device address as 
a dummy code when the communication from device to any other device is 
carried out. 
Further, in accordance with the first communication method according to 
this invention, in transmission, a route select code of a fixed length 
indicating a communication from a sub-device included in a device to any 
other device, a communication from a device to a sub-device included in 
any other device, or a communication from a device to any other device is 
inserted at a predetermined position of a data field of a transmit signal 
consisting of an address field and the data field to transmit, through the 
bi-directional bus, the transmit signal in which the route select code is 
inserted. In reception, the transmit signal is received through the 
bi-directional bus to detect the route select code from the received 
transmit signal to detect on the basis of the detected route select code 
whether a communication carried out is the communication from the 
sub-device included in the device to any other device, the communication 
from the device to the sub-device included in any other device, or the 
communication from the device to any other device. 
Further, in accordance with the second communication method according to 
this invention, a route select code is inserted into a data field of a 
transmit signal consisting of a header field, a master address field, a 
slave address field, a control field and the data field. 
Further, in accordance with the third communication method according to 
this invention, in transmission from a device to any other device, a 
sub-device address of a route select code consisting of a header operand 
and the sub-device address is transmitted as a dummy code. In reception, 
whether a communication carried out is communication from sub-device 
included in device to any other device, communication from device to a 
sub-device included in any other device, or a communication from a device 
to any other device is detected on the basis of the header operand, and a 
source or destination sub-device is specified on the basis of the 
sub-device address. When communication from device to any other device is 
carried out, the sub-device address is recognized as a dummy code. 
Further, in the fourth communication method according to this invention, 
the kind of the route select code is indicated by a text header of a route 
select code consisting of the text header, a header operand, and a 
sub-device address. 
Further, in accordance with the first bi-directional bus system according 
to this invention, respective transmit signal formation means of a 
plurality of devices insert a route select code of a fixed length 
indicating a communication from a sub-device included in a device to any 
other device, a communication from a device to a sub-device included in 
any other device, or a communication from a device to any other device at 
a predetermined position of data field of a transmit signal consisting of 
address field and the data field to form a transmit signal. The bus output 
means outputs this transmit signal to the bi-directional bus. 
Further, in accordance with the second bi-directional bus system according 
to this invention, transmit signal formation means of device forms a 
transmit signal in accordance with an operation content inputted from user 
interface means. 
Further, in accordance with the third bi-directional bus system, respective 
bus input means of a plurality of devices receive, through a 
bi-directional bus, a transmit signal consisting of an address field and a 
data field and including a route select code of a fixed length inserted at 
a predetermined position of the data field. The control means detects the 
route select code from the transmit signal received by the bus input means 
to detect on the basis of the detected route select code whether a 
communication carried out is communication from sub-device included in 
device to any other device, communication from the device to sub-device 
included in any other device, or communication from device to any other 
device. 
Further, in accordance with the fourth bi-directional bus system according 
to this invention, the control means of the device controls the AV signal 
switching means through the internal communication means on the basis of a 
received control command. The AV signal switching means switches 
input/output destination of an inputted/outputted audio signal/video 
signal. 
Further, in accordance with the fifth bi-directional bus system according 
to this invention, the control means of the device converts the same 
control command to an internal control command of control contents 
corresponding to various controlled system sub-devices by using a Table 
for converting a control command received by the bus input means to an 
internal control command for controlling the sub-device to transmit any 
internal control command to the sub-device through the internal 
communication means. 
In addition, in accordance with the sixth bi-directional bus system 
according to this invention, each transmit signal formation means of a 
plurality of devices inserts a path select code indicating a communication 
from a sub-device included in a device to any other device, a 
communication from a device to a sub-device included in any other device, 
or a communication from a device to any other device, and indicating a 
source sub-device address, a destination sub-device address, or a dummy 
code at a predetermined position of a transmit signal consisting of an 
address field and a data field to form a transmit signal. The bus output 
means outputs this transmit signal to the bi-directional bus. The bus 
input means receives the transmit signal through the bi-directional bus. 
The control means detects the route select code from the received transmit 
signal to detect on the detected route select code whether a communication 
carried out is communication from sub-device included in device, 
communication from device to sub-device included in any other device, or 
communication from device to any other device, and to specify a source or 
destination sub-device, or to recognize a dummy code.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of a transmitting method, a receiving method, and a 
communication method for a bi-directional bus system and a bi-directional 
bus system will now be described with reference to the attached drawings. 
In the embodiment, this invention is applied to D2B (Audio, Video and 
audiovisual systems Domestic Digital Bus) standardized by the publication 
103 of the so-called IEC, or a Home Bus System (hereinafter abbreviated as 
HBS) standardized by ET-2101 of EIAJ. 
A bi-directional bus system to which this invention is applied has a 
configuration such that a television image receiver (hereinafter each 
abbreviated as TV) 10 which is a device, video tape recorders (hereinafter 
abbreviated as VDP) 20, 30 which are a device, and a video deck player 
(hereinafter abbreviated as VDP) 40 which is a device are connected to 
each other through a bi-directional bus 1, as shown in FIG. 6, for 
example. 
The TV10 includes therein, as a sub-device, as shown in the above-mentioned 
FIG. 6, a tuner 10a adapted to receive a television (broadcasting) signal 
to reproduce a video signal and an audio signal therefrom, a TV monitor 
10b for displaying a picture based on the video signal reproduced at the 
tuner 10a, and an amplifier 10c for amplifying the audio signal reproduced 
by the tuner 10a, and further comprises, as a sub-device, a switch box 10d 
for outputting a video signal/audio signal (hereinafter referred to as an 
AV signal) from the tuner 10a, or delivering the AV signal inputted from 
the external to the tuner 10a and the TV monitor 10b. 
Further, the VTR 20 includes as a sub-device therein, as shown in the 
above-mentioned FIG. 1, a video deck 20a adapted for recording an AV 
signal onto a magnetic tape, or reproducing the AV signal therefrom, and a 
tuner 20b adapted to receive a television (broadcasting) signal to 
reproduce an AV signal therefrom, and further comprises, as a sub-device, 
a switch box 20c adapted for outputting an AV signal from the video deck 
20a or the tuner 20b to the external, or delivering an AV signal inputted 
from the external to the video deck 20a. 
Further, the VTR30 includes therein, as a sub-device, a video deck 30a, a 
tuner 30b, and a switch box 30c similarly to the above-described VTR20, 
In addition, the VDP 40 includes, as a sub-device, a video player 40a for 
reproducing an AV signal from an optical disk, 
In this bi-directional bus system, e.g., video signals reproduced by VTR20, 
VTR30, VDP40 are delivered to the TV10 to display a picture based on this 
video signal, In actual terms, the switch box 10d of the TV10 and the 
switch box 20c of the VTR20 are connected by an AV signal line L1, the 
switch box 10d of the TV10 and the switch box 30c of the VTR30 are 
connected by an AV signal line L2, and the switch box 10d of the TV10 and 
the video player 40a are connected by an AV signal line L3, viz,, AV 
signal lines L1, L2, L3 are wired in a star form with the TV10 being as a 
center. Accordingly, AV signals reproduced by VTR20, VTR30, VDP40 are 
respectively delivered to the TV monitor 10b through the AV signal lines 
L1, L2, L3 and the switch box 10d. Thus, pictures corresponding thereto 
are displayed on the TV monitor 10b. Further, e.g., an AV signal 
reproduced by the video player 40a is delivered to the video deck 20a 
through the AV signal line L3, the switch box 10d, the AV signal line L1, 
and the switch box 20c. Thus, they are recorded (image-recorded) onto a 
magnetic tape. 
Further, in this bi-directional bus system, e.g., the TV10 (device) 
controls, through the bi-directional bus, VTRs20, 30, VDP40 (devices) or 
video decks 20a, 30a, video player 40a, switch box 20c, 30c (sub-devices) 
included therein, or transmits, through the bi-directional bus 1, data 
indicating the operating states (statuses) of these equipments (devices or 
sub-devices). 
In actual terms, the TV10 comprises, as shown in FIG. 7, for example, a 
microprocessor 12 for controlling the tuners 10a.about.switch box 10d 
through the internal control bus 11, a user interface unit 13 for 
inputting operation contents operated by user to the microprocessor 12, 
and a bus interface circuit 14 for inputting a transmit signal consisting 
of control commands for controlling other devices and sub-devices thereof 
or data from the bi-directional bus 1 and outputting it thereto. 
Further, the VTR20 comprises, as shown in the above-mentioned FIG. 7, a 
microprocessor 22 for controlling the video deck 20a.about.switch box 20c 
through an internal control bus 21, a user interface unit 23 for inputting 
operation contents operated by user to the microprocessor 22, and a bus 
interface circuit 24 for inputting a transmit signal from the 
bi-directional bus 1 or outputting it thereto. Further, VTR30, VDP40 
similarly comprise a microprocessor and a bus interface circuit (not 
shown), etc. 
In operation, when, e.g., user operates the user interface unit 13 of the 
TV10 for the purpose of viewing, on the TV10, a picture based on a video 
signal reproduced by the VTR20, the microprocessor 12 of the TV10 forms a 
transmit signal in accordance with an operation content to transmit this 
transmit signal to the VTR20 through the bus interface circuit 14 and the 
bi-directional bus 1. The microprocessor 22 of the VTR20 carries out a 
control to play (reproduce) the video deck 20a through the internal 
control bus 21 on the basis of the transmit signal received by the bus 
interface circuit 24, and controls the switch box 20c so that an AV signal 
reproduced by the video deck 20a is delivered to the TV10. 
Namely, the user interface unit 13 comprises, as shown in the 
above-mentioned FIG. 7, an operation unit 13a provided with, e.g., a key 
switch, etc., and a display unit 13b provided with, e.g., a light emitting 
diode, etc. The operation unit 13a delivers a signal corresponding to an 
operation content that user has operated by using a key switch, etc. to 
the microprocessor through the internal control bus 11. 
The microprocessor 12 comprises, as shown in the above-mentioned FIG. 7, a 
Read Only Memory (hereinafter referred to as ROM) in which command Tables 
for converting received control commands which will be described later to 
internal control commands for controlling the tuner 10a.about.switch box 
10d or various programs are stored, a Central Processing Unit (hereinafter 
referred to as a CPU) for executing the program stored in the ROM12a, a 
Random Access Memory (hereinafter referred to as a RAM) 12c for storing 
result of the execution, or the like and an I/O circuit 12d adapted to 
interface with the tuner 10a.about.bus interface circuit 14. Further, the 
CPU12b generates a control command for controlling, e.g., VTR20 on the 
basis of a signal delivered from the operation unit 13a through the 
internal control bus 11, the I/O circuit 12d to deliver the control 
command thus generated to the bus interface circuit 14. 
The bus interface circuit 14 employs, e.g., so called a CSMA/CD (Carrier 
Sense Multiple Access with Collision Detection) as an access system for 
the bi-directional bus 1, and is connected to the bi-directional bus 1 
through a connector standardized, e.g., by so called IEC/SC48B 
(Secretariat) 202. 
In more practical sense, this connector comprises, as shown in FIG. 8A, two 
sockets 2, 3. As shown in FIG. 8B, contacts 2a, 2b for signal, a contact 
2c for earth of the socket 2, and contacts 3a, 3b for signal and contact 
3c for earth of the socket 3 are connected to each other within the 
connector. Further, contacts 2a and 2b are connected through a switch 2d 
and a terminating resistor (e.g., 120 m ohm) 4, and contacts 3a and 3b are 
connected through a switch 3d and the terminating resistor 4. 
Connectors constructed in this way are respectively provided every 
respective devices such as TV10, etc, Like connectors provided in the 
VTR20, for example, when a plug of the bi-directional bus 1 from the TV10 
and a plug of the bi-directional bus 1 from the VTR30 are respectively 
inserted into sockets 2, 3, the switches 2d, 3d are opened so that the 
terminating resistor 4 is cut off. As a result, a transmit signal from the 
TV10 is delivered to the bus interface circuit 24 of the VTR20, and is 
delivered to VTR30 or VDP40 of the succeeding stage. 
The format of a transmit signal transmitted on the bi-directional bus 1 
will now be described. The format of this transmit signal is substantially 
in conformity with the format of D2B described in the prior art, and 
control commands or data for controlling a destination sub-device, etc. 
are caused to have a frame structure as shown in FIG. 9. Thus, control 
commands and data of such structure are transmitted. 
Namely, one frame consists of a header field 51 for specifying the header 
indicating the leading portion of the frame, a master address field 52 for 
specifying a source device address, a slave address field 53 for 
specifying a destination device address, a control field 54 for specifying 
a control bit indicating a communication, etc. in the state where 
destination device is in lock state, or in the state where the destination 
device is in non-lock state, and a data field 55 for specifying control 
commands or data. 
The header of the header field 51 is in conformity with the D2B described 
in the prior art (see FIG. 2), and consists of a start bit of 1 bit for 
providing synchronization, and mode bits for prescribing a transmission 
speed or the number of bytes of the data field 55. 
The source device address of the master address field 52 is in conformity 
with the D2B described in the prior art, and consists of master address 
bits of 12 bits for specifying a source device address, and a parity bit 
of 1 bit. 
The destination device address of the slave address field 53 is in 
conformity with the D2B described in the prior art, and consists of slave 
address bits of 12 bits for specifying a destination device address, and 
an acknowledge bit of one bit for sending acknowledge from the destination 
device. 
The content of the control field 54 is substantially in conformity with the 
D2B described in the prior art, and consists of control bits of 4 bits 
indicating the lock state or the non-lock state, and specifying whether 
the data field 55 is control command or data, a parity bit of 1 bit, and 
an acknowledge bit of 1 bit. It is to be noted that as the control bit, 
there are used only code "E"h (h indicates hexadecimal notation) 
indicating write in a non-lock state of the control command, code "B"h 
indicating write in lock state of data, and code "F"h indicating write in 
a non-lock state, which are codes from master to slave of codes 
standardized in D2B. 
In the data field 55, data bits of 8 bits, end of data bit of 1 bit, and 
parity bit of 1 bit are repeated as occasions demands in conformity with 
the D2B described in the prior art. When it is assumed that data bits are 
assumed to be data #1, #2, #3 . . . from the beginning in order, a route 
select code of a fixed length, i.e., 24 bits indicating a communication 
from a sub-device included in a device to any other device, a 
communication from a device to a sub-device included in any other device, 
or a communication from a device to any other device is assigned to data 
#1.about.data #3 which are 3 bytes from the beginning as shown in the 
above-mentioned FIG. 9, for example, at a predetermined position of the 
data field 55. In addition, control commands, etc. are assigned to data 
#4. 
This routs select code consists of, as shown in the above-described FIG. 9, 
for example, a text header of 8 bits, a header operand comprised of 8 bits 
indicating communication from sub-device included in device to any other 
device, communication from device to sub-device included in any other 
device, or communication from device to any other device, and a sub-device 
address comprised of 8 bits indicating a Source Sub-Device Address 
(hereinafter referred to as SSDA) or Destination Sub-device Address 
(hereinafter referred to as DSDA). The text header is assigned to data #1 
as "AB"h to discriminate from OPC "Begin 2" (code "BD"h), OPC "Begin 1" 
("BC"h), OPC "Begin 0" ("BB"h) used in the conventional D2B. 
The header operand (hereinafter referred to as HDOPR) subsequent to the 
text header is assigned to data #2. For example, as shown in FIG. 10, by 
bits b.sub.1, b.sub.0 of the lower order 2 bits (b.sub.7 is the most 
significant bit (MSB)), communication from sub-device included in device 
to any other device (hereinafter referred to as communication from 
sub-device to device), communication from device to sub-device included in 
any other device (hereinafter referred to as communication from device to 
sub-device), or communication from device to any other device is 
designated. In more practical sense, b.sub.1 =0, b.sub.0 =1 indicates 
communication from sub-device to device, b.sub.1 =1, b.sub.0 =0 indicates 
communication from device to sub-device, and b.sub.1 =1, b.sub.0 =1 
indicates communication from device to device. Namely, in this 
bi-directional bus system, communication from a sub-device included in a 
device to a sub-device included in any other device used in the 
conventional D2B is not carried out. In other words, HDOPR where b.sub.1 
=0 and b.sub.0 =0 is not used. 
Accordingly, in carrying out communication from device to sub-device, e.g., 
sending a control command for playing, e.g., video deck 20a from TV10 
(device) to video deck 20a included in VTR 20 (other device), the 
microprocessor 12 of the TV10 assigns an address of TV10 as master address 
bits to the master address field 52, assigns an address of VTR20 as slave 
address bits to the slave address field 53, and assigns code "E"h 
indicating writing of the control command from master to slave to the 
control field 54. Further, the microprocessor 12 assigns code "AB" h as a 
text header to data #1, assigns a code (b.sub.1 =1, b.sub.0 =0) indicating 
communication from device to sub-device to data #2 as HDOPR, and assigns 
an address of video deck 20a to data #3 as DSDA. Further, in the 
microprocessor 12 assigns code "C3"h for playing, e.g., the video deck to 
data #4 subsequent thereto as OPC, and assigns code "75"h indicating 
forward to data #5 as OPR. 
Further, in carrying out communication from sub-device to device, e.g., VTR 
which has received, e.g., control command of play informs TV10 of the 
status of the video deck 20a (sub-device), the microprocessor 22 of the 
VTR20 assigns as shown in FIG. 11B, for example, address of VTR20 to the 
master address field 52 as master address bits, assigns address of TV10 to 
the slave address field 53 as a slave address bits, and assigns, e.g., 
code "E"h indicating write of control command from master to slave to the 
control field 54. Further, the microprocessor 22 assigns code "AB"h to 
data #1 as a text header, assigns code (b.sub.1 =0, b.sub.0 =1 indicating 
communication from sub-device to device to data #2 as HDOPR, and assigns 
address of video deck 20a to data #3 as SSDA. Further, the microprocessor 
22 assigns, to data #4, as OPC, e.g., code "C3"h indicating the 
above-described play, which indicates that, e.g., the video deck 20a is in 
a reproducing state, and assigns code "75"h indicating forward to data #5 
as OPR. 
In addition, in carrying out communication from device to device, e.g., 
allowing the power supply of VTR20 to be turned OFF from TV10, the 
microprocessor 12 of TV10 assigns, as shown in FIG. 11C, for example, 
address of TV10 to master address field 52 as a master address, assigns 
address of VTR20 to the slave address field 53 as slave address bits, and 
assigns, e.g., code "E"h indicating write of control command from master 
to slave to control field 54. Further, the microprocessor 12 assigns code 
"AB"h to data #1 as a text header, and assigns code (b.sub.1 =1, b.sub.0 
=1) indicating communication from device to device to data #2 as HDOPR. 
Meanwhile, in this case, since communication relating the sub-device is not 
included, i.e., an address of the sub-device is unnecessary, the 
microprocessor 12 assigns a dummy code, e.g., code "7F"h to data #3. 
Further, the microprocessor 12 assigns, e.g., code "A0"h indicating 
standby to data #4 as OPC, and assigns code "70"h indicating ON to data #5 
as OPR. Namely, in communication from device to device, the sub-device 
address is caused to be dummy code, thereby permitting a route select code 
consisting of text header, HDOPR and sub-device address to have a fixed 
length irrespective of communication route. 
A transmit signal having a frame structure as described above is delivered 
from the microprocessor 12 to the bus interface circuit 14. The bus 
interface circuit 14 detects presence or absence of so called a carrier on 
the bi-directional bus 1 to transmit the transmit signal to VTR20, 30 and 
VDP40, etc. through the bi-directional bus 1 when there is no carrier, 
i.e., the bi-directional bus 1 is empty. 
For example, the bus interface circuit 24 of the VTR20 receive the transmit 
signal, and delivers the received transmit signal to the microprocessor 
22. The microprocessor 22 executes program (software) stored in, e.g., ROM 
22a to detects, from the transmit signal, the route select code inserted 
at a predetermined position of the data field 55 to detect on the basis of 
the detected route select code whether communication carried out is 
communication from sub-device included in device to any other device, 
communication from device to sub-device included in any other device, or 
communication from device to any other device. 
In actual terms, the microprocessor 22 detects, on the basis of the master 
address bits of the master address fields 52 and the slave address bits of 
the slave address field 53 of the transmit signal, that this transmit 
signal is a transmit signal for the microprocessor 22 from, e.g., TV10, 
and detects, on the basis of the code of the control field 54, that this 
code indicates write of the control command from master to slave. It is to 
be noted that microprocessors of VTR30 and VDP40 detect that a current 
communication is not a communication for VTR or VDP from the fact that the 
slave address bits do not corresponds to their own addresses, thus not to 
carry out the operation corresponding to that transmit signal. 
Further, the microprocessor 22 detects, on the basis of the text header 
assigned to data #1 of the data field 55, that a current code is not OPC 
"Begin 2" (code "BD"h), OPC "Begin 1" ("BC"h), or OPC "Begin 0" ("BB"h) 
used in the conventional D2B by, e.g., code "AB"h, and detects the kind of 
communications on the basis of HDOPR assigned to data #2, i.e., when, 
e.g., the lower order 2 bits are 1, 0 (b.sub.1 =1, b.sub.0 =0), the 
microprocessor 22 detects that a current communication is communication 
from device to sub-device; when those bits are b.sub.1 =0, b.sub.0 =1, it 
detects that current communication is communication from sub-device to 
device, and when those bits are b.sub.1 =1, b.sub.0 =1, it detects that 
current communication is communication from device to device. Namely, even 
if a transmit signal in conformity with the conventional D2B is 
transmitted through the same bi-directional bus 1, discrimination 
therebetween can be made. In other words, by carrying out transmission 
with the kind of the route select code being specified to the text header 
of the route select code, it is possible to transmit a transmit signal in 
conformity with the conventional D2B and a transmit signal to which this 
invention is applied through the same bi-directional bus 1. 
At the time of communication from device to sub-device, the microprocessor 
22 recognizes that DSDA is assigned to data #3. At the time of 
communication from sub-device to device, the microprocessor 22 recognizes 
that SSDA is assigned to data #3. Further, at the time of communication 
from device to device, the microprocessor 22 recognizes that data #3 is 
dummy code "7F"h. In addition, the microprocessor 22 specifies, on the 
basis of DSDA assigned to, e.g., data #3, that a current control is, e.g., 
control for video deck 20a. 
Meanwhile, respective equipments (devices) such as VTR20, etc. have a 
command Table for converting control commands to internal control commands 
for controlling sub-devices every sub-devices that those devices include 
therein, thus to convert (decode) the same control command to internal 
control command of control contents corresponding to various control led 
system sub-devices. In more practical sense, in a ROM 22a of the 
microprocessor 22, for example, a command Table for video deck 20a, a 
deck/player command Table and a command Table for tuner 20b as shown in 
FIGS. 12, 13, for example, and a tuner command Table as shown in FIGS. 14, 
15, for example, are stored. The microprocessor 22 decodes control 
commands assigned to data #4, #5 of the data field 55 into internal 
control commands for controlling the video deck 20a.about.switch box 20c 
on the basis of these command Tables to control the video deck 
20a.about.switch box 20c through the internal control bus on the basis of 
the internal control commands. Namely, e.g., in OPC of the control 
commands, code "CO"h indicates a repeat in the deck/player command, as 
shown in the above-mentioned FIG. 12, indicates control of the band in the 
tuner commands, as shown in the above-mentioned FIG. 14, indicates control 
of contrast (not shown) in the video command, and indicates control of 
volume (not shown) in the audio command. In other words, a command Table 
determined by a default value of a sub-device specified by DSDA is used. 
As a result, code of the same control command can be commonly used so as 
to cope with various sub-devices. Thus, the control command can be 
shortened. In addition, since the control command can be shortened, the 
transmission efficiency can be improved. 
For example, as shown in the above-mentioned FIG. 11A, when DSDA is video 
deck 20a, OPC of the control command is code "C3"h, and OPR is code "75"h, 
the microprocessor 22 of the VTR20 decodes a control command into an 
internal control command indicating play and forward by using the 
deck/player command Table to carry out a control so that the video deck 
20a conducts a reproducing operation through the internal control bus 21, 
and to carry out a control so that an AV signal from the video deck 20a is 
delivered to the switch box 10d of TV10 through switch box 20c. In this 
way, communication from TV10 (device) to video deck 20a (sub-device) of 
VTR20 is carried out. Thus, user can view, on TV10, a picture based on the 
AV signal reproduced by the VTR20, 
Further, as shown in the above-mentioned FIG. 11B, for example, when SSDA 
is video deck 20a, OPC of control command is "C3"h (play) and OPR is code 
"75"h (forward), the microprocessor 12 of TV10 receives the information 
that video deck 20a of VTR20 is in a reproducing state, Thus, 
communication from video deck 20a (sub-device) of VTR20 to TV10 (device) 
is carried out. 
Further, as shown in the above-mentioned FIG. 11C, for example, when 
sub-device address (data #3) is dummy code, OPC of control command is code 
"A0"h (standby), and OPR is code "70"h (ON), the microprocessor 22 of 
VTR20 controls a power supply (not, shown) so that its control state 
shifts from ON state to standby state. Thus, communication from TV10 
(device) to VTR20 (device) is carried out, so control of the power supply 
of VTR20 is conducted. 
As described above, in this bi-directional system, OPC of control command 
is transmitted in the state assigned to data #4 of the data field 55 at 
all times, For example, microprocessor 22 of a destination device can 
control video deck 20a.about.switch box 20c or ON/OFF of power supply. In 
other words, in the format used in the conventional D2B, the position of 
OPC of the control command varies in dependency upon a communication route 
(path). As a result, software for decoding control commands was complex. 
However, the position of OPC of control command is fixed, thereby making 
it possible to simplify software, In addition, software in forming a frame 
of a transmit signal can be also more simplified by fixing the position of 
OPC of the control command as compared to the prior art, 
It is to be noted that this invention is not, limited to the 
above-described embodiment, but can be applied to, e.g., a communication 
to send a request from a device to a sub-device to send an answer from the 
sub-device to the device, e.g., a communication for automatically 
informing the status of device, or the like. In addition, it is needles to 
say that this invention can be applied to e.g., a bi-directional bus 
system adapted to control AV equipment except for D2B or HBS. 
As is apparent from the foregoing description, in accordance with this 
invention, a route select code of a fixed length indicating communication 
from a sub-device included in a device to any other device, communication 
from a device to a sub-device included in any other device, or 
communication from a device to any other device is inserted at a 
predetermined position of a data field of a transmit signal consisting of 
an address field and the data field to transmit, through a bi-directional 
bus, the transmit signal in which the route select code is inserted, 
thereby making it possible to fix the position in the data field of the 
control command irrespective of the communication route (path). Thus, 
software constituting a frame of a transmit signal can be simplified. 
Further, in this invention, in communication from a device to any other 
device, a sub-device address of a route select code consisting of a header 
operand and a sub-device address is caused to be a dummy code, thereby 
permitting the position in data field of the control command to be the 
same in the case of communication from a sub-device included in a device 
to any other device, and communication from a device to a sub-device 
included in any other device. Thus, software constituting a frame of a 
transmit signal can be simplified. 
Further, in this invention, a transmit signal consisting of an address 
field and a data field and including a path select code of a fixed length 
inserted at a predetermined position of the data field is received through 
a bi-directional bus to detect the route select code from the received 
transmit signal to detect on the basis of the detected route select code 
whether a communication carried out is communication from sub-device 
included in device to any other device, communication from device to 
sub-device included in any other device, or communication from device to 
device, thereby making it possible to decode data at a predetermined 
position of data field as a control command. Thus, software for decoding 
control commands can be simplified. 
Further, in this invention, whether a communication carried out is a 
communication sub-device included in a device to any other device, a 
communication from a device to a sub-device included in any other device, 
or a communication from a device to any other device is detected on the 
basis of a header operand of a route select signal consisting of the 
header operand and the sub-device address to specify a source or 
destination sub-device on the basis of the sub-device address, and to 
recognize the sub-device address as a dummy code when communication from 
the device to any other device is carried out, thereby permitting the 
position in the data field of the control command to be the same as that 
in the case of the communication from sub-device included in device to any 
other device and the communication from device to sub-device included in 
any other device. Thus, the software for decoding the control command can 
be simplified. 
Further, in this invention, a route select code is inserted into data field 
of a transmit signal consisting of a header field, a master address field, 
a slave address field, a control field, and a data field, thereby making 
it possible to fix the position of the data field of the control command. 
Thus, software for the transmitting device and the receiving device can be 
simplified. 
Further, in this invention, the kind of route select codes is indicated by 
a text header of a route select code consisting of text header, header 
operand and sub-device address, thereby making it possible to transmit, 
through the same bi-directional bus, a transmit signal in conformity with, 
e.g., conventional D2B and a transmit signal to which this invention is 
applied. 
Further, in this invention, transmit signal formation means of device forms 
a transmit signal in accordance with an operation content inputted from 
user interface means, thereby making it possible to carry out, e.g., an 
operation that user controls any other device from user interface means of 
device. 
Further, in this invention, control means of device controls the AV signal 
switching means through the internal communication means on the basis of a 
received control command. The AV signal switching means switches 
input/output destination of an inputted/outputted audio signal/video 
signal to thereby carry out, e.g., selective switching between a plurality 
of VTRs, thus permitting user to view on TV monitor a picture based on an 
AV signal reproduced by the video deck of a selected VTR. 
In addition, control means of device decodes the same control command into 
an internal control command of control contents corresponding to various 
controlled system sub-devices by using a Table for converting control 
commands received by bus input means to internal control commands for 
controlling the sub-device to transmit this internal control command to 
sub-device through internal communication means, thereby making it 
possible to commonly use the same control command for different kinds of 
sub-devices. As a result, the kind of control commands can be reduced, and 
the control command can be shortened. Thus, the transmission efficiency 
can be improved.