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Contents
1. DCF 4 COMMAND FIELDS je E34 M M 4 FIG 2 DATA FIELD SERVICE ADDRESS TYPE FOLLOWER ADDRESS ADDRESS BS yaya FIG 2B US Patent Jan 27 1998 Sheet 2 of 3 5 712 852 U S Patent Jan 27 1998 Sheet 3 of 3 5 712 852 450 Start init IST 2 F 55 MSA FFF H FI6 4 5 712 852 1 D2B DEVICE STATION ADDRESS INITIALIZATION STARTING WITH STORED ADDRESS The invention relates to a single channel communication bus system The system includes a communication bus having a plurality of stations connected to it The stations can communicate with one another via the communication bus Each station has a unique station address assigned The stations include an interface circuit which is adapted to call any destination station by generating a destination station address of said destination station The interface circuit is also adapted to receive an acknowledge signal which is transmitted by the relevant destination station if the station address of said destination station corresponds to the trans mitted destination station address The interface circuit of a station is further adapted to perform an initialisation pro gram under the control of which the interface circuit is able to generate and transmit a plurality of different destination station addresses in a determined sequence Such generation and transmission are discontinued upon absence of an acknowledge signal The desti2. field MO subsequently the default station address MSA and finally the destination station address SSA of the destination station with which communication is desired are sent Detection of receipt of absence of an acknowledge code takes place in a step 462 If no acknowl 10 15 35 45 55 65 6 edge code is received in the acknowledge code field ACI so that ACI 0 then in next step 464 the counter value is raised by 1 NAC NAC 1 In the subsequent step 466 itis tested whether absence of an acknowledge bit has been detected three times If so then in a next step 468 the master station address is set to the destination station address SSA including the then present follower address FA The initiali sation procedure will thereafter end in step 70 However if in step 466 it is detected that the counter value NAC is less than three the procedure starts again at step 460 Each time the count value NAC will be increased unless in step 462 it is detected that an acknowledge bit has been received in the acknowledge code field ACI so that ACI 1 Whenever an acknowledge code occurs ACI 1 1 this means that a station is connected to the communi cation bus which has the same service address SA type address TA and follower address FA as the transmitting master station Therefore the follower address FA is increased by one in step 472 FA FA 1 In a next step 74 it is tested whether the follower address FA differs fr
3. is ultimately received If this command field is not the last field the transmission will be continued by sending the next 10 15 25 35 45 55 65 4 command field If this field is the last field the communi cation operation is terminated Subsequently a new com munication operation can be started It is to be noted that parity bits are also transmitted in the different fields so as to protect the information from trans mission errors E 3 The station address In FIG 2B the general structure of a station address is shown It comprises a service address SA a type address TA and a follower address FA The service address SA comprises for example four bits and can thus distinguish sixteen services for example an audio video service a washing service a cooking baking service etc The type address TA comprises for example five bits so that thirty two stations can be distinguished within one service For example within the washing service a distinction can be made between a washing machine a drier a dish washer etc and within tile audio video service a distinction can be made between a TV set a TV monitor a tuner a video recorder etc It will often occur in practice that the user has a number of apparatuses of the same type for example two or more video recorders The follower address FA enables him to distinguish between these apparatuses of the same type This follower address comprises for example
4. the initialisation As already noted in the foregoing section a station address comprises a service address SA a type address TA and a follower address FA Service address SA and type address TA have been assigned by manufacturers and in practice the manufacturer programs them in the station address memory 22 33 63 of the interface circuit 22 32 42 As said before the follower address FA will be set to zero or to 111 by the manufacturer and programming of the follower address FA will be done in use and thus does not take place until after the relevant apparatus has been con nected to the communication bus 1 by means of the interface circuit The further embodiment of an initialisation program comprises for example the steps shown in FIG 4 which are performed as soon as the apparatus is switched on More particularly after start of the initialisation START INIT in step 450 the present follower address FA is used to set a test value TST in second step 452 Further in said second step 452 the destination station address SSA is made equal to the present master station address MSA of which the parts SA TA are fixed and the part FA is to be found Thereafter the master station address MSA is set to a default value e g FFF H which mean 1111 1111 1111 in hexa decimal notation Further in a next step 454 a not acknowledge counter NAC are set to zero In the next program step 460 the start bit ST the mode bits of the mode
5. 2 3 and 4 are connected to this communication bus 1 Each station 2 3 and 4 respectively comprises an apparatus 21 31 and 41 respectively which is connected to the data lines 11 and 12 by means of an interface circuit 22 32 42 As already noted such an apparatus may be a TV monitor a video recorder an audio recorder an audio tuner etc The communication bus 1 is intended to transmit control signals from a first station to a second station Any station may act as a master station and thereby all other stations act as destination stations Some stations will act as transmitters 5 712 852 3 of data some act as receivers of data Furthermore all kinds of mixed or alternating situations are possible The commu nication operations on the communication bus which will herein be described are performed by the interface circuits 22 32 and 42 A so called microcontroller MAB 5051 extensively described in chapter 3 of Single Chip Micro controllers User Manual 1988 Philips Electronic Compo nents and Materials for example be used as an interface circuit To be able to distinguish the different stations each interface circuit has a programmable non volatile memory 23 33 43 in which a station address is stored A typical station address comprises twelve bits E 2 The message structure The general structure of a message structure on an information level which structure is extensively described in Chapter 11 of the User Manual poin
6. 50 451 452 454 455 442 489 485 395 200 02 287 200 16 281 200 1 421 01 365 189 02 SDAT SERIAL INTERFACE 22 NJN VOLATILE MEMORY MEMORY 23 APPARATUS 21 2 STATION CIRCUIT 32 NON VOLATILE ters 3 and 11 Primary Examiner Wellington Chin Assistant Examiner Melissa Kay Carman Attorney Agent or Firm Anne E Barschall 57 ABSTRACT A single channel communication bus system has stations which communicate with each other via the bus Each station must have a unique address which is initialized during a system initialization In order to facilitate initialization a manufacturer determined address is stored in a non volatile memory Search for a unique address for each station begins with the address stored in the non volatile memory 7 Claims 3 Drawing Sheets 1 INTERFACE T CRCUT 42 INTERFACE NON VOLATILE CIRCUIT MEMORY 43 APPARATUS 4 4 STATION 47 STATION U S Patent Jan 27 1998 Sheet 1 of 3 5 712 852 SDAT 12 C MUNICATION SDAT 1 h BUS INTERFACE INTERFACE 11 22 CIRCUIT 32 CRCUIT 42 neus NON VOLATILE NON VOLATILE NON VOLATILE CIRCUIT MEMORY MEM MEMORY 23 APPARATUS 21 31 41 2 STATION 3 STATION 4 STATION ACKNOWLEDGE MODE ACKNONLEDGE ACKNOWLEDGE ACKNOWLEDGE START O ws 3p STRUCTURE 2 XPDODDOD DM k DCF DCF
7. again Whenever an acknowledge code occurs ACI 1 this means that a station is connected to the communication bus which has the same service address type address and follower address as the transmitting master station When an acknowledge code has been received enough times the counter value CNT will have the value of four which means that one of the stations has definitely a station address which should not be used by this master station Therefore after detection that the counter value CNT24 a step 72 is carried out wherein the follower address FA is increased by one In a next step 74 it is tested whether the follower address FA differs from the test value TST if so then the initialisation procedure is started again by resetting the counter values CNT and NAC to zero in step 54 If the test value TST equals the follower address FA then all different positions of the latter have been used If the follower address FA consists of three bits then after 8 trials with different values for FA the starting value TST will be reached due to the setting of TST equal to FA in step 52 In such a situation the initialisation procedure is aborted END in step 70 and said station cannot communicate via the bus 1 In the above example four times a message will be sent on the bus and at maximum one failure acknowledge of a message will be accepted for permitting use of an address by an apparatus connected to the bus 1 E 5 A further embodiment of
8. hereinbefore is repeated up to the moment where no acknowledge signal will be received by the newly added station This means that there is no station having this address chosen by the newly added station and thus this address is unique As soon as this situation occurs the newly added station will adopt this unique address as its own The above described station address initialisation can be used in a D2B system which for instance has been described in U S Pat No 4 429 384 From the description of the D2B system in this U S Pat No 4 429 384 can be deduced that the D2B should perform in a reliable way in a low cost and possible noisy environment Experience has shown that signals on buses sometimes deteriorate which as a conse quence means that the above initialisation procedure can be puined Some station on the bus system may sent an acknowledge signal to inform the newly added station that the address send by itis not unique but if such acknowledge signal is deteriorated then the newly added station will adopt said address as its own but said address is not unique As a result communication between these two stations and other 10 15 35 45 55 65 2 stations will be disastrous because if one of the two stations is addressed by another station both stations will respond and mostly in different ways because each station might be a totally difference type of device Also in this case no proper initialisation will take p
9. lace Further the Dutch patent application 8900717 discloses that the message including the destination address also comprises the address of the master station to be initialized thereby the destination station address and the master station address are the same In practice it has become clear that use of the same address for the master station and the destination station is problematic because the receiving part of the master station might read the destination station address and consequently would control the transmitting part of the master station to send an acknowledge signal to itself It is the object of the invention to provide a communi cation bus system wherein the above described problems are mitigated and address initialisation is carried in a robust reliable noise insensitive way Therefore the single channel communication bus system is characterized in that each station has a non volatile memory for storing the address assigned to said station whereby upon start of the initialisation program the genera tion and transmission of the different destination station addresses starting with the address stored previously in said non volatile memory It has been found in practice that use of the address stored previously in said non volatile memory as a start address in the initialisation procedure the number of attempts to find a unique address is substantially reduced This reduction is even more drastic if the configuration i e the
10. ledge counter NAC are set to Zero In a next program step 56 the counter CNT is checked whether its value is equal or greater than 4 Subsequently in step 58 the counter CNT is increased by one Reason for this will be explained later on In the next program step 60 the start bit ST the mode bits of the mode field MO subsequently the default station address MSA and finally the destination station address SSA of the destination station with which communication is desired are sent Detection of receipt of absence of an acknowledge code takes place in a step 62 If no acknowl edge is received code in the acknowledge code field ACI so that ACI 0 then in a next step 64 the counter value NAC is raised by 1 NAC NAC 1 Subsequent step 66 tests whether absence of an acknowledge bit has been detected three times If so then in a next step 68 the master station 5 712 852 5 address is set to the destination station address SSA includ ing the then present follower address FA The initialisation procedure will thereafter end in step 70 However if in step 66 it is detected that the counter value NAC is less thanthree the procedure starts again at step 56 Each time the count value NAC will be increased unless in step 62 it is detected that an acknowledge bit has been received in the acknowledge code field ACI so that ACI 1 the counter value CNT is tested in a step 56 If the counter value CNT is less than 4 the steps 58 to 66 are performed
11. nation station address that is the last that has been generated and transmitted is assigned as the master station address to said station Such a single channel communication bus system is known from the Dutch patent application No 8900717 which has been published on Oct 16 1990 In said patent application has been described how a new device or station is added to the bus system When the station has been switched on a software protocol in said station will initialize the procedure to find a unique address for said station The station address initialisation involves in fact two steps A first one is choosing an address and the second one is verifying whether that address is unique In order to find out whether said address is unique the added station sends a chosen address on the bus to all other stations which are connected to the bus system Each station which has already been active in the bus system checks whether the address sent by the newly added station corresponds with its own address or not In the first situation the station that identifies the address sent by the newly added device as its own will send back to the newly added station an acknowledge signal So if the newly added station receives an acknowledge signal it can verify that the address chosen by it previously is not unique As a result in a second cycle the newly added station will choose another address different from the first chosen one and the protocol as described
12. ode field If this second acknowledge code is not received by the master station the communica tion may be discontinued If the master station has received this second acknowledge code a data field DF will be sent In this data field the master DF station transmits data to the destination station or vice versa The data field DF com prises one single or a plurality of command fields DCF Each command field comprises one or more data bytes DB which represents the actual information an EOD field end of data the end of the data byte s of a command field and or indicating whether a further command field DCF II DCF III follows this command field DCF I and an acknowledge code field in which the destination station indicates that the information has been received correctly If no acknowledge code is received this may mean that i the actual information is mutilated due to transmission errors ii the destination station is switched off after the transmission of the control code or iii the destination station is not capable of receiving and buffering the data byte for example because the processing of this information takes too long In all these cases i c not receiving an acknowledge code AC the master station is set to its repetitive position for sending once again e g the whole message Another possibility is to resend upon absence of an acknowledge code ACIII the relevant command field until the acknowledge code
13. om one preset address of the station VCR 1 to the second preset address of the station VCR 2 If this second address is acknowledged in a succeeding initialization procedure which is triggered by the user by e g switching power off and on again then again the master station address is set to the default address FFF If the user does not interfere anymore then the station continues to operate with the default address T claim 1 A single channel communication bus system compris ing a a communication bus b a plurality of stations connected to the communication bus which plurality of stations can communicate with one another via the communication bus each respec tive one of the plurality of stations requiring a respec tive unique station address and including 1 a respective interface circuit for A calling a destination station from amongst the plurality of stations by generating and transmit ting a destination station address of said destina tion station 5 712 852 7 for receiving an acknowledge signal that is trans mitted by said destination station if the respective unique station address of said destination station corresponds to the transmitted destination address C performing an initialisation program under the control of which the interface circuit generates and transmits at least one of a plurality of different destination addresses according to a predetermined sequence start ing from a star
14. om the test value TST if so then the initialisation procedure is started again by setting the counter value NAC to zero in step 454 If the test value TST equals the follower address FA then all different posi tions of the latter have been used If the follower address FA consists of three bits then after 8 trials with different values for FA the starting value TST will be reached due to the setting of TST equal to FA in step 452 In such a situation the initialisation procedure is aborted END in step 470 and said station cannot communicate via the bus 1 Of course different possibilities exist for finding unique addresses for the stations by use of majority votes The above given examples shall by no means limit the scope of the invention which apart from test values to be used or of efficiency of the initialisation program does not make any influence on the invention as such In the situation that a station has address setting means to be controlled by the user e g a switch for setting the address of a VCR to VCR 1 or VCR 2 the flow charts as shown in FIG 3 and FIG 4 can be simplified substantially The steps 72 and 74 or 472 and 474 can be dispensed with and thus the variable item TST can be dispensed with too see step 52 and 452 At the end in step 70 or 476 the master station address will be the default address FFF which should be signalled to the user via e g a display The user then can throw a switch in order to change fr
15. omprises a fixed part which depends on the type of station and a variable part which comprises a fixed number of bits 4 Asingle channel communication bus system as claimed in claim 3 characterized in that the fixed number of bits is three and in the initialisation program after each generation and transmission of one of the plurality of different desti nation station addresses when such generation and transmission is acknowledged by another station on the bus system the variable part is incremented by one and to create a next one of the plurality of different desti nation station addresses and initialisation is aborted upon generation and transmission and acknowledgment of all possible eight addresses in the variable part 5 A single channel communication bus system as claimed in claim 2 wherein each of the plurality of destination addresses comprises a fixed part which depends on the type of station and a variable part which comprises a fixed number of bits 6 The system of claim 1 wherein communication along the single channel bus is according to a D2B protocol 7 Asingle channel communication bus system as claimed in claim 5 characterized in that the fixed number of bits is three and in the initialisation program after each generation and transmission of one of the plurality of different desti nation station addresses when such generation and transmission is acknowledged by another station on the bus system the va
16. riable part is incremented by one to create a next one of the plurality of different destination station addresses and initialisation is aborted upon generation and transmission and acknowledgment of all possible eight addresses in the variable part
17. stations connected to the bus has not been changed An embodiment of the invention is characterized in that the station before sending a destination station address during the initialisation program adopts a default address which is forbidden to be used by any station operating after initialisation in the bus system Upon start of the initialisa tion procedure the master station address is given a default address which cannot be used under normal operation i c after initialisation by any of the other stations connected to the bus As a consequence any station to be initialised will not react to its own transmitted messages Upon determina tion of a unique address the default address will be replaced by the new found unique address The invention will further be explained in detail by use of drawings and corresponding descriptions given herebelow thereby in the drawings FIG 1 shows diagrammatically the general structure of a single channel communication system FIGS 2A and 2B show diagrammatically the message structure as used on the communication bus FIG 3 shows a flow chart for determining the station address of a station in accordance with the invention FIG 4 shows initialization program E 1 General structure of the communication bus system FIG 1 shows diagrammatically a single channel com munication bus system It comprises a serial communication bus 1 consisting of two data lines 11 and 12 In this case three stations
18. t value discontinues said generation and transmission of the at least one of the plurality of different destination station addresses upon absence of an acknowledge signal y assigns as the respective unique station address of the respective one of the plurality of stations a last one of at least one of the plurality of different destination station addresses which is the last that was generated and transmitted and 8 stores the respective unique station address in a non volatile fashion for use as a next start value in a future initialisation and ii a respective non volatile memory for storing the start value and next start value as the respective unique address of the respective one of the plurality of stations such that upon start of the initialisation program the generation and transmission of the at least one of the plurality of different destination station addresses starts with the start value without added bits 2 A single channel communication bus system as claimed in claim 1 wherein at least one of the plurality of stations before transmitting the at least one of the plurality of different destination station addresses in the initialisation program adopts a default address that is forbidden to be used by any station except during initialisation in the bus system 3 A single channel communication bus system as claimed in claim 1 wherein each of the plurality of destination 10 15 35 8 addresses c
19. ted out hereabove is denoted in FIG 2A Such a message structure starts with a start bit ST It is followed by a mode field MO in which a number of so called mode indication bits is transmitted A typical number of mode indication bits is three They indicate the rate at which the following information will be transmitted In fact a limited number of standardized trans mitter frequencies has been defined This mode field is followed by a master station address field MSA In this field the twelve bit master station address is transmitted from the station wishing to transmit information to a destination station The twelve bit destination station address is subse quently transmitted in the destination station address field SSA If a station recognizes the destination station address it transmits an acknowledge code in an acknowledge code field ACL If this acknowledge code is not received it means that the said destination station is not present or does not function or that the destination station address is received in a mutilated non recognizable form by the destination sta tion In these cases the communication may be discontinued each time after the acknowledge code field If the destination station has transmitted an acknowledge code the master station transmits a control code of for example four bits in a control field CF After reception of this control code the destination station again transmits an acknowledge code in an acknowledge c
20. three bits so that eight apparatuses of the same type can be distinguished E 4 The initialisation As already noted in the foregoing section a station address comprises a service address SA a type address TA and a follower address FA Service address SA and type address TA have been assigned by manufacturers and in practice the manufacturer programs them in the station address memory 23 33 43 of the interface circuit 22 32 42 In practice the follower address FA will be set to zero or to 111 by the manufacturer and programming of the follower address FA will be done in use and thus does not take place until after the relevant apparatus has been con nected to the communication bus 1 by means of the interface circuit To this end this interface circuit has an initialisation program which comprises for example the steps shown in FIG 3 and which is performed as soon as the apparatus is switched on More particularly after start of the initialisation STARTINIT in step 50 the present follower address FA is used to set a test value TST in a second step 52 TST FA Further in said second step 52 the destination station address SSA is made equal to the present master station address MSA of which the parts SA TA are fixed and the part FA is to be found Thereafter the master station address MSA is set to a default value e g FFF H which means 1111 1111 1111 in hexadecimal notation Further in a next step 54 a counter CNT and a not acknow
21. xx US005712852A United States Patent 1j Patent Number 5 712 852 Wilson 45 Date of Patent Jan 27 1998 54 D2B DEVICE STATION ADDRESS 56 References Cited INITIALIZATION STARTING WITH STORED ADDRESS U S PATENT DOCUMENTS 4 429 384 1 1984 Kaplinsky een 370 442 75 Inventor Neil A Wilson Weybridge United 4 661 902 4 1987 Hochsprung et al 395 800 Kingdom 5 150 464 9 1992 Sidhu etal 395 200 1 73 Assignee DB2 Systems Company Limited FOREIGN PATENT DOCUMENTS Redhill Great Britain 0537814 4 1993 European Pat Off HO4L 29 06 8900717 3 1989 Netherlands HO4B 3 50 21 Appl No 374 680 8900717 10 1990 Netherlands 22 PCT Filed Jun 24 1994 0 537814A1 9 1991 Netherlands HO4L 29 06 OTHER PUBLICATIONS 86 PCT No PCT IB94 00174 MAB 5051 Single Chip Microcontrollers User Manual 371 Date Jan 25 1995 1988 Philips Electronic Components and Materials Chap 102 e Date Jan 25 1995 87 PCT Pub No WO95 01026 PCT Pub Date Jan 5 1995 30 Foreign Application Priority Data Jun 25 1993 EP European Pat Off 93201840 51 Ibt CEP sinisisi HO4L 12 403 52 US 370 451 370 457 370 489 395 281 395 421 01 58 Field of Search 370 85 1 85 5 C MUNICATION 4 SDAT 1 BUS 370 85 11 85 4 85 9 85 2 85 7 457 447 449 4
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