Security module for a serial communications device

1. A security module for a serial communications device, the security module comprising:

a receive data, RXD, input interface for receiving data from a serial communications bus;

a transmit data, TXD, output interface for transmitting data to the serial communications bus;

wherein the security module is configured to:

receive a message from the serial communications bus via the RXD input interface;

compare the message with one or more conditions;

upon detection that a condition has been violated, output an error-signal to the serial communications bus via the TXD output interface, wherein the error-signal identifies one or more parameters relating to the condition;

compare (i) the error-signal that is output to the serial communications bus via the TXD output interface; with (ii) a bus-error-signal that is received via the RXD input interface; and

output an error-check-signal to the serial communications bus via the TXD output interface, wherein the error-check-signal is indicative of whether or not there is a difference between the error-signal and the bus-error-signal;

wherein the error-signal comprises: a first-identifier relating to the condition; and a second-identifier relating to the condition;

wherein the bus-error-signal comprises: a bus-first-identifier relating to the condition; and a bus-second-identifier relating to the condition; and

wherein the error-check-signal comprises:

a first-error-check-signal, which is indicative of whether or not there is a difference between: (i) the first-identifier of the error-signal; and (ii) the bus-first-identifier of the bus-error-signal; and

a second-error-check-signal, which is indicative of whether or not there is a difference between: (i) the second-identifier of the error-signal; and (ii) the bus-second-identifier of the bus-error-signal.

2. The security module of claim 1 , wherein the one or more parameters relating to the condition can take one of at least three different values.

3. The security module of claim 1 , wherein the error-signal comprises an error-identifier of one or more conditions that have been violated.

4. The security module of claim 1 , wherein the security module is associated with a serial communications node, and the error-signal comprises a node-identifier of the serial communications node.

5. The security module of claim 1 , wherein the error-signal comprises a security-module-identifier of the security module.

6. The security module of claim 1 , wherein the error-check-signal comprises one or more dominant bits if there is a difference between the error-signal and the bus-error-signal.

7. The security module of claim 1 , wherein:

the security module is associated with a serial communications node;

the first-identifier comprises a node-identifier of the serial communications node;

the bus-first-identifier comprises a bus-node-identifier of one or more serial communications nodes;

the second-identifier comprises an error-identifier of one or more conditions that have been violated; and

the bus-second-identifier comprises a bus-error-identifier of one or more conditions that have been violated.

8. The security module of claim 1 , wherein the error-signal comprises a plurality of bit positions, and wherein each of the bit positions uniquely identifies a particular condition or a particular node-identifier.

9. The security module of claim 8 , wherein:

the security module is associated with a serial communications node;

the error-signal comprises a node-identifier of the serial communications node;

the node-identifier comprises a plurality of bit positions;

each of the bit positions of the node-identifier uniquely identifies a particular node;

the error-signal comprises an error-identifier of one or more s that have been violated;

the error-identifier comprises a plurality of bit positions;

each of the bit positions of the error-identifier uniquely identifies a particular condition.

10. The security module of claim 1 , wherein the error-signal comprises a plurality of bit positions, and wherein the error-signal comprises a dominant bit value at a predetermined bit position.

11. The security module of claim 10 , wherein the predetermined bit position is the first bit position.

12. The security module of claim 1 , wherein:

the serial communications device in a CAN XL node; and

the serial communications bus is a CAN XL bus.

13. A serial communications node comprising a security module, the security module comprising:

a receive data, RXD, input interface for receiving data from a serial communications bus;

a transmit data, TXD, output interface for transmitting data to the serial communications bus;

wherein the security module is configured to:

receive a message from the serial communications bus via the RXD input interface;

compare the message with one or more conditions;

upon detection that a condition has been violated, output an error-signal to the serial communications bus via the TXD output interface, wherein the error-signal identifies one or more parameters relating to the condition and wherein the error-signal comprises:

an error-identifier of one or more conditions that have been violated; and

a node-identifier of the serial communications node;

compare (i) the error-signal that is output to the serial communications bus via the TXD output interface; with (ii) a bus-error-signal that is received via the RXD input interface; and

output an error-check-signal to the serial communications bus via the TXD output interface, wherein the error-check-signal is indicative of whether or not there is a difference between the error-signal and the bus-error-signal;

wherein the error-signal comprises: the node-identifier of the serial communications node;

and the error-identifier of the one or more conditions that have been violated;

wherein the bus-error-signal comprises: a bus-node-identifier of one or more serial communications nodes; and a bus-error-identifier of one or more conditions that have been violated; and

wherein the error-check-signal comprises:

a first-error-check-signal, which is indicative of whether or not there is a difference between: (i) the node-identifier of the error-signal; and (ii) the bus-node-identifier of the bus-error-signal; and

a second-error-check-signal, which is indicative of whether or not there is a difference between: (i) the error-identifier of the error-signal; and (ii) the bus-error-identifier of the bus-error-signal.

14. A method of outputting an error-signal to a serial communications bus, the method comprising:

receiving a message from the serial communications bus;

comparing the message with one or more conditions;

upon detection that a condition has been violated, outputting an error-signal to the serial communications bus, wherein the error-signal identifies one or more parameters relating to the condition;

comparing (i) the error-signal that is output to the serial communications bus; with (ii) a bus-error-signal that is received; and

outputting an error-check-signal to the serial communications bus, wherein the error-check-signal is indicative of whether or not there is a difference between the error-signal and the bus-error-signal;

wherein the error-signal comprises: a first-identifier relating to the condition; and a second-identifier relating to the condition;

wherein the bus-error-signal comprises: a bus-first-identifier relating to the condition; and

a bus-second-identifier relating to the condition; and

wherein the error-check-signal comprises:

a first-error-check-signal, which is indicative of whether or not there is a difference between: (i) the first-identifier of the error-signal; and (ii) the bus-first-identifier of the bus-error-signal; and

a second-error-check-signal, which is indicative of whether or not there is a difference between: (i) the second-identifier of the error-signal; and (ii) the bus-second-identifier of the bus-error-signal.

15. The method of claim 14 , wherein the error-signal comprises an error-identifier of one or more conditions that have been violated.

16. The method of claim 14 , wherein the error-signal comprises a node-identifier of a serial communications node.

17. A security module for a serial communications device, the security module comprising:

a receive data, RXD, input interface for receiving data from a serial communications bus;

a transmit data, TXD, output interface for transmitting data to the serial communications bus;

wherein the security module is configured to:

receive a message from the serial communications bus via the RXD input interface;

compare the message with one or more conditions;

upon detection that a condition has been violated, output an error-signal to the serial communications bus via the TXD output interface, wherein the error-signal identifies one or more parameters relating to the condition, wherein the error-signal comprises a plurality of bit positions, and wherein each of the bit positions uniquely identifies a particular condition or a particular node-identifiers;

wherein:

the security module is associated with a serial communications node;

the error-signal comprises a node-identifier of the serial communications node;

the node-identifier comprises a plurality of bit positions;

each of the bit positions of the node-identifier uniquely identifies a particular node;

the error-signal comprises an error-identifier of one or more s that have been violated;

the error-identifier comprises a plurality of bit positions; and

each of the bit positions of the error-identifier uniquely identifies a particular condition.

18. The security module of claim 17 , wherein the one or more parameters relating to the condition can take one of at least three different values.

19. The security module of claim 17 , wherein the error-signal comprises an error-identifier of one or more conditions that have been violated.

20. The security module of claim 17 , wherein the security module is associated with a serial communications node, and the error-signal comprises a node-identifier of the serial communications node.