Automatic can address allocation method

Details Automatic can address allocation method Automatic can address allocation method

1998-03-26

2001-04-10

Rinehart, Mark H. (Department: 2756)

Electrical computers and digital processing systems: multicomput

Bused computer networking

C709S227000, C709S253000, C710S004000, C710S009000, C710S220000

Reexamination Certificate

active

06216172

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a method of automatically allocating addresses in a controller area network (CAN) including a plurality of bus subscribers, one of which serves as the controlling station for initiating address allocation, whereby each bus subscriber is assigned a unique serial number memorized in a non-volatile memory of the bus subscriber and whereby each bus subscriber has a writeable non-volatile memory.
BACKGROUND OF THE INVENTION
A controller area network (CAN) is a computer network serving measurement and control instrumentation intercommunication in technical fields, more particularly in motor vehicles and in measurement and control technology. The CAN bus is a two-wire bus. Whilst motor vehicles usually always contain the same measurement and control instrumentation, the addresses of which are dedicated, in measurement and control technology the number of bus subscribers allocated addresses in each case varies and is initially unknown.
Hitherto CAN bus subscriber addresses were set by means of hardware switches by the user, this harboring the risk of the same address being allocated multiply due to a wrong setting. In addition to this the setting needs to be made before other configurations can be implemented which causes additional trouble to the user. Furthermore, address allocation is an activity, the use of which is not immediately apparent to the user since it is lastly of no concern to him how the individual bus subscribers swap information.
Described in EP 0 221 303 B1 is a method of automatically allocating addresses in a computer network. However, this known method requires a bus having more than two wires as well as the existence of a host processor, it thus not being suitable for a CAN environment, i.e. in a network in which only one two-wire bus is available and all bus subscribers have substantially the same priority.
OBJECT OF THE INVENTION
The object of the invention is to define a method which permits automatic address allocation in a CAN environment.
SUMMARY OF THE INVENTION
In accordance with the invention this object is achieved by the following steps in the method:
each bus subscriber still to be allocated an address, generates a first random value for a provisional address on system power up;
on receiving a request to commence address allocation sent by the controlling station a telegram claiming the provisional address dictated by the first random value is written into the CAN send buffer of each bus subscriber and a wait initiated for authorization to access the bus in sending the telegram;
if a bus subscriber receives a telegram claiming an address which fails to agree with its own provisional address. This address is entered into a list of accredited bus subscribers held in a memory of the receiving bus subscriber;
if before sending its own telegram a bus subscriber receives a telegram claiming an address which agrees with its own provisional address, a new first random value is generated for a provisional address and a telegram claiming this provisional address is written into the CAN send buffer;
if the telegram claiming its own provisional address is sent before a telegram of some other bus subscriber claiming the same provisional address is received, its own provisional address is accepted as the final address in the list of accredited bus subscribers and deposited in the writeable non-volatile memory.
In the method in accordance with the invention generating and allocating the addresses is done by the individual bus subscribers themselves; the controlling station substantially merely dictating initiation of address allocation. The method is thus particularly suitable for a bus system having essentially equal priority subscribers, and a two-wire bus is sufficient for application of the method.
In one advantageous aspect of the method in accordance with the invention each bus subscriber generates together with the first random value a second random value for a delay time and the telegram claiming the provisional address dictated by the first random value is written into the CAN send buffer on time-out of the delay time dictated by the second random value. The staggered time in claiming random generated provisional addresses caused by the random generated delay time reduces the probability of two or more bus subscribers receiving the same address.
Further advantageous aspects of the method in accordance with the invention are characterized in the sub-claims.


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