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HA-I01.01

Part description

Current development revision

This document describes the protocol used for automatic assignment of device identification numbers (CAN-IDs) to newly attached bus devices.

Mode of operation

When a HA-CAN bus device is manufactured, the device identification number (CAN-ID) of it is not yet known. For ease of use, it is desirable that this does not have to be programmed into the device manually when the device is attached, but automatically assigned by the control software. The control software keeps a list of all attached devices anyways (together with their configuration), so it can assign the next free CAN-ID to any new device that is seen. The operator can then manually configure this device as required, and at a time suiting operation's needs, while the device is already active on the bus, but not hindering other bus transactions.

For this functionality, a specific CAN-ID is defined under which the Automatic CAN Address Assignment (ACAA) datagrams are transmitted. This CAN-ID is reserved, and will not be used for regular bus device communications. Only ACAA traffic is permitted using this CAN-ID. The ACAA process is designed to be fast enough for assigning a "real" CAN-ID to a new device on the bus before another new device is added in all practical situations, given the intent of this whole project.

Protocol description

The ACAA protocol consists of two steps. First, a request for a CAN address is sent to the bus using the specified ACAA CAN ID, and under this CAN ID the address is transmitted to the client. Afterwards, to ensure correct transmission and receipt of the assigned address, a check transmission is sent to the client and acknowledged by it. Only after successful reception of this check packet is the client allowed to store the new address as its fixed CAN identity, and only after receipt of the check acknowledgment is the ACAA server allowed to permanently register this CAN ID for the new device.

If assignment and verification fails in any step, the new client device must start the process from the beginning. The server is in this case expected to hand out only a limited number of addresses through ACAA, and, if assignment repeatedly fails, stop responding to ACAA queries and request operator intervention. If the assignment process failes from ACAA server viewpoint after handing out the new CAN ID, it must mark the respective ID as blocked, and request operator intervention before marking it as clear to hand out again.

CAN-ID

Device ID 121 has been assigned and reserved for the ACAA traffic.

Protocol

Note: Server should wait 20 to 30 ms between step 2 and 3 to allow for client's adjustment of address configuration.

CategoryElectronics

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