GB2407898A - Issuing commands selectively to a plurality of zones e.g. on a train - Google Patents

Abstract

A control system for issuing local commands selectively to a plurality of zones e.g. for operating selected doors of a train. A command system 14 generates a command containing information relating to the zones to which a local command is to be issued, a transmission medium 16 transmits the command, and a plurality of blocks 12 are connected in series by the transmission medium, each block assigned to one of the zones. Each block 12 receives the command, issues a local command to the zone if required by the command, modifies the command to account for receipt of the command by the block, and transmits the command to a subsequent block in the series. Different alternative command structures are described: using one wire per zone; binary coding (multiplexing); or serial communication. Each block may modify the command by decrementing the indication of the number of zones to which the local command is to be issued, e.g. by decrementing the number of signals transmitted in parallel, or the number of pulses in a train.

Description

DISTRIBUTION OF NETWORK CONFIGURATION SPECIFIC COMMANDS TECHNICAL FIELD OF THE INVENTION The invention relates to a system and method for distributing network configuration specific commands More specifically, the invention relates to a control system for issuing commands selectively to a plurality of zones ofa train or similar entity. BACKGROUND ART Trains typically include control systems which distribute control commands to some or all of the cars making up the train. For example, such train comands include commands for controlling components and systems such as brakes, traction, doors and lighting. Some of these train commands are required to be directed to or acted on by only certain cars within the train. One example of this is a control command for Selective Door Operation. Such a command controls the opening and closing of the train doors by selectively operating the doors according to the length of the station platform currently in use by the train. This command may need to be sent through the train but only issued to or acted upon from a certain car onwards and/or up to a certain car within the series of train cars. This typically means each car needs to know where it is in the train configuration (i.e. which position it occupies in the series of cars making up the train). One means for providing this function is to hardwire the train so that such commands are only routed to the cars to which they are required to be sent. This has the disadvantage that the distribution of commands is determined by the way each car is wired. If the train is reconfigured by changing the arrangement of cars (e.g. additional cars coupled, cars turned, intermediate cars added), the wiring or wiring connectors or other components need to be reconfigured as well, resulting in delay and expense. Another solution is to provide a supervisory/management system which is programmed with the configuration of the train. Such systems typically include a computer with software to describe the train configuration and control the issuance of train commands. Reconfiguring the train thus requires modifying the software to reflect the new train configuration. However, such systems are complex and difficult to implement to achieve the necessary level of integrity and safety to meet safety requirements. Systems based on train networks are known which do not need physical reconfiguration when the train is reconfigured. However, these systems are also complex and difficult to implement to achieve high reliability and integrity to satisfy the safety requirements. The system requires configuration input from an exterior source (e.g. the computer network) which makes the command dependant on other functions and systems of the train, resulting in the greater risk of unavailability and unreliability. SUMMARY OF THE INVENTION The invention aims at providing an improved system for distributing network configuration specific commands. According to a first aspect of the present invention, there is provided a control system for issuing commands selectively to a plurality of zones, the control system comprising: a first command system for generating a command, the command containing information relating to the zones to which a local command is to be issued; a transmission medium for transmitting the command; and a plurality of blocks connected in a series by the transmission medium, each block being assigned to one of the zones; each block receiving the command, issuing a local command to the zone if required by the command, modifying the command to account for receipt of the command by the block, and transmitting the command to a subsequent block in the series. The command may indicate the number of zones to which the local command is to be issued. In one embodiment, each block in a zone to which the local command is to be issued modifies the command by modifying the indication of the number of zones to which the local command is to be issued to reduce the number of zones by one. The command may comprise a plurality of signals transmitted in parallel, and the transmission medium may comprise a plurality of lines, including at least one line for each zone. Advantageously, each block in a zone to which the command is to be issued may modify the command by reducing the number of signals transmitted in parallel. This may be accomplished by connecting block to the transmission medium at a first port and a second port, where each block in a zone to which the local command is to be issued connects n lines of the transmission medium connected to the first port to n-1 lines of the transmission medium connected to the second port. The command may also comprise a binary coded signal or a sequence of pulses. Advantageously, the number of pulses in the command may be related to the number of zones to which the local command is to be issued. This may be accomplished wherein each block modifies the command to account for receipt of the command by that block by reducing the number of pulses in the command. The control system may further comprise a second command system, the first and second command systems being located at opposite ends of the series of blocks. Each block may be connected to the transmission medium via two ports, each block being capable of receiving a command from either port and transmitting the modified command from the other port. The blocks may generate an error signal to indicate a data integrity error in the command received by the block, and may generate a sleeping failure signal if the block issues a command to a zone to which the block is assigned. Advantageously, the control system may be applied to issue commands for opening and/or closing the doors of a train. According to a second aspect of the invention, there is provided a control block for receiving a command and selectively issuing a control signal to at least one component based on the command, the control block comprising: a first port connected to a transmission medium for receiving the command; - a sensing element for sensing the presence of the command on the transmission medium; - a first logic means for issuing the control signal to the component if required by the command; - a second logic means for modifying the command to account for receipt of the command by the control block; and a second port connected to the transmission medium for transmitting the modified command on the transmission medium. Advantageously, the control block may be capable of receiving the command at the second port and transmitting the modified command from the first port. According to another aspect of the invention, there is provided a method for directing commands to selected zones arranged to receive the command in a sequence, the method comprising: generating a command containing information relating to the zones to which a local command is to be issued; transmitting the command to a first zone; issuing the local command to the zone only if required by the command; - modifying the command to account for receipt of the command by the first zone; retransmitting the modified command to a subsequent zone; and - repeating the issuing, modifying, and retransmitting steps until all zones have received the command. The invention provides a system and method for directing commands to selected zones without the need for hardwired configuration of the zones, modification of software to reflect the zone configuration, or configuration input from an exterior source. This avoids problems when the system is reconfigured by changing the arrangement of zones, resulting in increased integrity, reliability, and safety of the system. BRIEF DESCRIPTION OF THE FIGURES Other advantages and features of the invention will become more apparent from the following description of specific embodiments of the invention given as non-restrictive examples only and represented in the accompanying drawings in which: Figure 1 is a block diagram of an embodiment of a system for distributing network configuration specific commands shown deployed in a train. Figures 2-4 show an embodiment of modular block 12 implemented using relays for distributing a command where all cars along the train up to a preselected car receive the command but the remaining cars do not receive the command. Figures 5 A and 5B show an embodiment of modular block 12 implemented using relays and diodes for use with a binary coded command structure. Figure 6A and 6B show an embodiment of modular block 12 implemented using relays for use with a serial communication protocol. Figures 7A-7C show additional features which can be used with the embodiment of Figures 5A-5B; Figure 8 shows a further modification to the embodiment of Figures 5A-5B for detecting sleeping failures. Figure 9 shows a further modification to the embodiment of Figures 5A-5B to provide additional verification logic. DETAILED DESCRIPTION OF EMBODIMENTS With reference to Figure 1, a train, tram or other articulated vehicle 10 is shown with four cars, including a cab at each end of the train. The train includes a modular block 12 in each car or zone and two command systems 14 interconnected by train wiring or bus 16. The train may include multiple command systems 14 or a single command system, for issuing control commands to the train. The command system 14 issues commands onto the train bus 16 for transmission to the modular blocks 12. The modular blocks 12 receive the commands, issue the local command 18 to the car if required, and also distribute the commands along the train. The command system 14 may be a computer system or simply a train operator control, typically located a leading car, often at both ends of the train. The bus 16 may comprise a parallel bus with a separate wire for each modular block 12 or a serial bus or any other type of communication channel suitable for use in a train environment. The modular block 12 functions as an internal command conversion block. The connections shown on the left and right of block 12 can be both inputs and outputs at the same time. The block 12 senses all these lines to detect from which side the command is given. When block 12 knows which side is the commanding side, it configures itself so that the side from which the command is coming becomes the input side and the other side becomes the output side. Block 12 determines, based on the input, if the command is to be executed by the car or zone in which the block is located. If so, block 12 issues the command onto the "local command" output 18. Block 12 assumes that it is the first block to receive the command and thus does not need to know where it is located within the train configuration. Block 12 converts an incoming command by generating a local command for its own car or zone, and generating the command transmitted to the next car or zone knowing the next block 12 will assume it is the first one to receive this command. Thus, all blocks 12 in the train look at the command content as if they were the first car or zone in the command structure, and then generate the command for the next block. The command itself contains information relating to the cars or zones to which it is to be issued. The command can be directed to any section, part, or component of the train. For example, the commands could be distributed to individual train "zones" where each zone may comprise a single car, several cars in a group, separate portions of a single car (e.g. front and back halves of a car), or individual components within a car (e.g. each door of a car). This requires one block 12 per zone that is to be separately addressed. An example of an application of a configuration specific command is for Selective Door Operation where a command is sent to the doors so that only the doors in the leading X cars can be released, while the remaining cars must remain unreleased. In other words car X must be given the command not to distribute the release beyond itself. The command structure used to transmit the control commands through the train may take many different forms. Different command structures result in differing requirements for the number of lines and varying complexity of the block 12. For example, possible command structures include the use of one wire per car (or more generally per zone), binary coding (also known as multiplexing), or serial communication, as described in below. A command structure having one wire available per car or zone results in a substantial amount of wiring (i.e. N wires for N zones) but permits complicated commands to be transmitted. For example, a command could be transmitted directed only to specific zones (e.g. car 1 = OK; car 2 = OK; car 3 = NOK; car 4 = OK; car 5 = OK; car 6 = NOK). Furthermore, the implementation of such a system is simple and can be achieved purely using relays or equivalent components. Figures 2-4 show an embodiment of modular block 12 implemented using relays for distributing a command where all zones along the train up to a preselected zone receive the command but the remaining zones do not receive the command. An example of an application of such a configuration specific command is Selective Door Operation (SDO) where a command is sent such that only the doors in the leading X cars can be released, while the remaining cars must remain unreleased. In other words, car X is given the command but is not to distribute the release beyond itself. In this embodiment, the train bus 16 includes a wire for each zone in the train. The modular block 12 includes two sensing relays 20 and 24, each having a set of ganged contacts 21 and 25, and each set of ganged contacts including a relay energizing contact 22 and 26 for energizing sensing relays 20 and 24, and a local command contact 23 and 27 for issuing a local command 18 to the zone in which the modular block 12 is located or assigned. Modular block 12 is connected on both sides to the train bus 16, shown as bus 16a on the left side and 16b on the right side. The ganged contacts 21 and 25 operate to connect individual wires within bus 16a to wires within bus 16b. In this embodiment, wires 28 and 29 provide electrical positive and negative (or phase and neutral) lines to power the relays and local commands. Figure 2 shows the status of the modular block 12 when no command is present on the bus 16. Both sensing relays 20 and 24 are de-energised and no local command 18 is present. Figure 3 shows a command on bus 16a. To better illustrate the operation of block 12, the lines or bus wires which are energized (e.g. have an electrical voltage on them) are shown thicker than the other lines. The command illustrated on bus 16a in Figure 3 has energised five of the individual lines 16al to 16a5, signifying that five more zones are to receive the command. The voltage on line 16al causes sensing relay 24 to be energized, which changes the position of the ganged contacts 25, 26 and 27. Contact 27 closes, issuing the local command to the zone. Contact 26 opens, precluding sensing relay 20 from becoming energized. Contacts 25 close, connecting line 16a2 of bus 16a to line 16bl of bus 16b. Similarly, line 16a3 is connected to line 16b2, line 16a4 is connected to line 16b3, and so on. This results in lines 16bl to 16b4 being energized. Thus, block 12 received a command on bus 16a signifying "five more zones to receive the command." Block 12 issued a local command to its zone and passed on the command to bus 16b, now modified to "four more zones to receive the command." In this way each block 12 passes the command along the train bus 16 to blocks further along the train, each block modifying the command to account for its having received the command so that only the number of blocks commanded to receive the command actually receive it. In the example shown in Figure 3, the fourth zone further along the train bus will receive the command "one more zone to receive the command" and will not pass on any command to blocks still further along the bus. Thus, the command itself contains information relating to the zones to which it is to be issued and is modified each time it passes from one zone to the next to account for having been received by each previous zone. Block 12 is designed to receive commands in either direction, i.e. coming from the left on bus 16a or from the right on bus 16b. This enables the blocks 12 to operate with a command system 14 located at either end of the train 10 without any modification or configuration required on the blocks. Figure 4 shows a command coming from the right on bus 16b. Command lines 16b 1 - 16b7 are energized signifying "seven more zones to receive the command." Sensing relay 20 is energized, a local command 18 is issued and the lines 16al-16a6 arc energized signifying "six more zones to receive the command." It is also possible to use binary coding (also known as multiplexing) to transmit the commands. In this case only M lines are needed to transmit the command to N zones, where M is the smallest integer for which 2<M>> N. In this case the possible content of one command is more limited as it must be a command related to the encoded zone. Possibilities include, for example, only giving the command to zone X, giving it to all zones except zone X, giving it to all zones up to and including (or up to but not including) the Xth zone, or giving it to all zones from and including (or from but not including) the Xth zone. Figures 5 A and 5B show an embodiment of modular block 12 implemented using relays and diodes for use with a binary coded command structure. In this example, the range of commands is from 0 to 15, and thus four lines are needed to account for the 16 available commands. These four lines are shown as bus 16c on the left and bus 16d on the right. Four logic relays I1-l4are shown corresponding to the four input bits o the binary coded commands. Each relay can be connected to one of the command lines of bus 16c or 16d by contacts of sensing relays 50 or 52 respectively. Relays I1-L each have a plurality of normally open and normally closed contacts wired to generate output bits O1-O4according to the following logic: O4= L and (I3or I2or I1) O3= L and not(I3) and not(I2) and not(l1) or I3and (I2or I1) 02= Ii and I2or not(I[iota]) and not(I2) and (I3 or I4) O1= (L or I3 or I2) and not(I1) When a command is received on bus 16c sensing relay 50 is energized through diodes 54, causing ganged contacts 50a of relay 50 to close. This also causes contact 50b to open preventing sensing relay 52 from energizing and contact 50c to close sending a local command 18 to the zone. The' closure of contacts 50a connects bus 16c to logic relays I-L and connects outputs O1-O4to bus 16d. Each energised line of bus 16c causes a corresponding logic relay to energise which results selected outputs O1-O4being energized according to the above logic. This results in the same command modification described above for the embodiment of Figures 2-4. For example, when block 12 receives a command on bus 16c signifying "four more zones to receive the command." This command is represented as "4" or binary "0100" and only line 16c3 of bus 16c is energized and so only logic relay I3is energized. As a result, output bits O1and 02are energized while O3and O4are de-energised. This output is represented as "3" or binary "0011" and lines 16dl and 16d2 of bus 16d are energized, signifying "three more zones to receive the command." This modified command is transmitted on bus 16d to the next block along the train bus 16. If the command is received on bus 16d, sensing relay 52 is energised connecting logic relays 11-L4to bus 16d and the outputs O1-O4to bus 16c via contacts 52a, but otherwise the block 12 operates as described above. Thus, the binary command contains information relating to the zones to which it is to be issued and is modified each time it passes from one zone to the next by modifying the binary code to account for having been received by each previous zone. It should be noted that the output on bus 16c or 16d corresponding to "no more zones to receive the command" is "0000" providing a fail safe position. The implemented logic shown in the embodiment of Figure 5 has been optimised to reduce the number of logical elements. When not all codes 0 to 15 are needed the functions can be further optimised, both towards reduced number of relays and contacts and towards increased data integrity, for example to generate an output equal to zero if the command input is out of range. Other means of improving the integrity of the system are described below. The embodiment shown in Figures 5 A and 5B is only one possible implementation of a binary coded command structure. Many other implementations will be apparent to those of skill in the art using well known techniques and alternatives. It should also be noted that the diodes could be implemented as relays, and/or the relays could be implemented using transistors or other electronic components. Another possibility is to use serial communication between the blocks. The specific protocol used for this serial communication will determine the level of complexity of the sender/receiver sub-blocks, as well as the complexity of the command structure. The number of wires needed is reduced as compared with the first embodiment and is defined by the type of serial link employed. Figure 6 A and 6B show an embodiment of modular block 12 implemented using relays for use with a serial communication protocol to give a command from a cab vehicle to a certain number of the leading cars or zones. For the sake of simplicity, a simple serial communication protocol is illustrated; the number of pulses on the bus 16 indicates the number of zones to receive the command. For example, X pulses are generated at the leading end of the network (e.g. the leading cab) and issued to the X leading zones. One line is needed for the command and one more line is used to undo (reset) the command. Many other protocols may also be used as will be apparent to those of skill in the art. The bus 16 comprises a command line (16el, 16fl) for transmitting the command signal and a reset line (16e2, 16f2) for resetting the command. The reset line is illustrated as active when low although other controls are possible. Block 12 includes sensing relays 61 and 62, latch relay 63 and local command relay 64, all with corresponding contacts designated a, b, c etc. Sensing relays 61 and 62 energise on the rising edge of pulses on command line 16el and 16fl respectively. Latch relay 63 energises when contacts 61a or 62a close and latches itself via contacts 63a. When the command pulse disappears (i.e. on a falling edge), contacts 61b and 62b close and relay 64 is energised. This causes relay 64 to latch via contact 64a and connects bus 16e and 16f via contact 64b so that any additional command pulses on bus 16 pass through the block 12. When relay 64 energises, contacts 64c open so that sensing relays 61 and 62 remain de-energised and contact 64d closes to issue a local command 18. The relay 64 remains energised until a reset pulse is transmitted on the reset line which signals the end of the current command. Thus, the block 12 does not transmit the first pulse of the command so that the number of transmitted pulses is one less than the number received. Each block along the train bus 16 receives a pulse train having one less pulse than the previous block. Thus, the command itself contains information relating to the zones to which it is to be issued and is modified each time it passes from one zone to the next by reducing the number of pulses to account for having been received by each previous zone. The basic designs described above may be modified to increase the integrity level of the command distribution. The aim of these optional modifications is lo improve the failure behaviour of the system by eliminating as many single points of failure as possible, and/or providing a fail safe failure mode. For binary coded designs of the type shown in Figures 5A-5B, the data integrity of the command can be improved by using conventional redundant binary coding techniques. An example is the addition of a parity status line used to perform a parity check on commands received. When a parity status line is used, the logic level of that line is generated so that the M+l bit word (i.e the command bits including the parity bit) has a preset parity. Another optional feature which can be used in conjunction with the parity status line is to include an additional data integrity check and put this information in an error signal for fault handling purposes. Figures 7A-7C show an example of a parity line and error signal used with the embodiment of Figures 5A-5B for increased system integrity. The binary command structure in this example includes a five bit command including a parity bit as an additional I/O to block 12. An additional line (16g5, 16h5) is included in bus 16 for transmission of an even parity bit. Parity input relay 70 is energised by the parity input bit Pi. Parity output relay 72 generates the parity output bit Po according to logic 73 which implements the following logic function: Po = not(L) and (I4and (I2and not(I1) or not(I2)) or not(L) and I2) or I4and I3 and (I2or not(I1)) The parity output signal Po is sent onwards on the train bus 16 via parity output contact 72a. Error relay 74 generates error signal Er to indicate a parity error on the incoming command according to logic 75 which implements the following logic function: Er = not( (not(l4) and not(l3) or I4and I3) and (not(I2) and (not(I[iota]) and not(Pi) or I1and Pi) or I2and (Ii and not(Pi) or not(I1) and Pi)) or (not(L and I3or I4and not(I3)) and (not(I2) and (h and not(Pi) or not(I1) and Pi) or I2and (not(I) and not(Pi) or I, and Pi)) ) A command error line 76 may optionally be included to feed back the error information to the command system 14 via error relay contact 74a. The local command may also be prevented from being sent by error relay contact 74b. The embodiment of Figure 7A-7C operates in other respects the same as that of Figures 5A-5B. In a serial communication design of the type shown in Figures 6A-6B, a communication protocol of conventional type employing handshaking and sender/receiver acknowledgement can be implemented to increase system integrity. In the one wire per zone design of the type shown in Figures 2-4, data integrity can be checked by verifying the command structure based on the known design constraints of the commands. For example, if the command is always "all zones from the first one until zone X", then a high signal on a given line can never be preceded by a low signal on that line. This can be implemented in a manner similar to the implementation shown in Figures 2-4. Sleeping failures where a component does not act upon a command may be detected, for example, by using a sleeping failure signal line which all blocks 12 activate whenever they issue a local command 18. Logic may be added to the command system 14 (or elsewhere in the system) which verifies that no signal is present on the sleeping failure signal line when no command has been issued, and/or additional logic may be added which verifies that a signal is present on this line whenever a command has been issued. Figure 8 shows a modification to the embodiment of Figures 5A-5B for detecting such sleeping failures. Contacts 50d and 52d of sensing relays 50 and 52 respectively (shown in Figure 5A) are added to block 12, for sending information indicating the issuance of a local command back to the command system 14 on an additional sleeping failure signal line 80. Figure 9 shows a further modification to provide verification logic to generate a system fault signal or alarm based on a sleeping failure signal. When a command is being transmitted on train bus 16 the relay 90 is energised and normally closed contact 90a is open so no fault signal is generated. When no command is being transmitted on train bus 16 the relay 90 is de-energised and normally closed contact 90a is closed. Any signal present on sleeping failure signal line 80, indicating that a local command is being issued by any of the blocks 12, will result in a sleeping fault signal 92 being generated. This fault signal 92 may indicate, for example, that a door is being commanded to open when it should not. The signal 94 which indicates whether a command is transmitted on bus 16 can come from command system 14 and/or a dedicated system such as a door control system in an occupied cab. The various embodiments described above have been illustrated using relay logic. It will be apparent to those of skill in the art that many other implementations are possible using well known techniques and alternatives. For example, these embodiments could be implemented using solid state circuits with transistors and other electronic components, field programmable gate arrays, application specific integrated circuits, or firmware or software in conjunction with computer processors, or any combination of the above. Many modifications may be made to the stmctures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention.

Claims (24)

1. A control system for issuing commands selectively to a plurality of zones, the control system comprising: - a first command system for generating a command, the command containing information relating to the zones to which a local command is to be issued; a transmission medium for transmitting the command; and a plurality of blocks connected in a series by the transmission medium, each block being assigned to one of the zones; each block receiving the command, issuing a local command to the zone if required by the command, modifying the command to account for receipt of the command by the block, and transmitting the command to a subsequent block in the senes.

2. The control system of claim 1, wherein the command indicates the number of zones to which the local command is to be issued.

3. The control system of claim 1 or claim 2, wherein each block in a zone to which the local command is to be issued modifies the command by modifying the indication of the number of zones to which the local command is to be issued to reduce the number of zones by one.

4. The control system of any of claims 1-3, wherein the command comprises a plurality of signals transmitted in parallel.

5. The control system of claim 4, wherein the transmission medium comprises a plurality of lines, including at least one line for each zone.

6. The control system of claim 5, wherein each block in a zone to which the command is to be issued modifies the command by reducing the number of signals transmitted in parallel.

7. The control system of claim 6, wherein each block is connected to the transmission medium at a first port and a second port, and wherein each block in a zone to which the local command is to be issued connects n lines o the transmission medium connected to the first port to n-1 lines of the transmission medium connected to the second port.

8. The control system of any of claims 1-3, wherein the command compnses a binary coded signal.

9. The control system of any of claims 1 -3, wherein the command comprises a sequence of pulses.

10. The control system of claim 9, wherein the number of pulses in the command is related to the number of zones to which the local command is to be issued.

1 1. The control system of claim 10, wherein each block modifies the command to account for receipt of the command by that block by reducing the number of pulses in the command.

12. The control system of any of claims 1-11, further comprising a second command system, the first and second command systems being located at opposite ends of the series of blocks.

13. The control system of claim 12, wherein each block is connected to the transmission medium via two ports, each block being capable of receiving a command from either port and transmitting the modified command from the other port.

14. The control system of any of claims 1-13, wherein each block generates an error signal to indicate a data integrity error in the command received by the block.

15. The control system of any of claims 1 -14, wherein each block generates a sleeping failure signal if the block issues a command to a zone to which the block is assigned.

16. The control system of any of claims 1-15, wherein the control system issues commands for opening and/or closing the doors of a train.

17. A control block for receiving a command and selectively issuing a control signal to at least one component based on the command, the control block comprising: a first port connected to a transmission medium for receiving the command; - a sensing element for sensing the presence of the command on the transmission medium; a first logic means for issuing the control signal to the component if required by the command; a second logic means for modifying the command to account for receipt of the command by the control block; and a second port connected to the transmission medium for transmitting the modified command on the transmission medium.

18. The control block of claim 17, wherein the control block is capable of receiving the command at the second port and transmitting the modified command from the first port.

19. The control block of claim 17 or claim 18, wherein the control block generates an error signal to indicate a data integrity error in the command received by the control block.

20. The control block of any of claims 17-19, wherein the control block generates a sleeping failure signal if the control block issues a command to a zone to which the control block is assigned.

21. The control block of any of claims 17-20, wherein the control block issues commands for opening and/or closing the doors of a train.

22. A method for directing commands to selected zones arranged to receive the command in a sequence, the method comprising: generating a command containing information relating to the zones to which a local command is to be issued; transmitting the command to a first zone; - issuing the local command to the zone only if required by the command; - modifying the command to account for receipt of the command by the first zone; - retransmitting the modified command to a subsequent zone; and - repeating the issuing, modifying, and retransmitting steps until all zones have received the command.

23. The method of claim 22, further comprising generating a sleeping failure signal when a local command is issued to a zone.

24. The method of claim 22 or claim 23, wherein the local command is for opening and/or closing the doors of a train.