Understanding the Kvaser Air Bridge Management Interface
The Kvaser Air Bridge Management Interface is an application-level request/response protocol that enables a user application to access the control and monitoring services of a Kvaser Air Bridge one-to-any device. Put simply, the Management Interface allows users to integrate the Air Bridge into their applications to take advantage of wireless connectivity and create more advanced solutions. By utilizing dedicated arbitration identifiers to separate itself from the rest of the bus load, the Management Interface is able to send and receive messages with the Air Bridge one-to-any that other nodes on the bus will automatically ignore. These arbitration identifiers are as follows:
Default Receiver ID: 0x1BC78FFF
This is the identifier for messages being sent to the Kvaser Air Bridge one-to-any.
Default Sender ID: 0x1BFFF8F1
This is the identifier for messages being sent from the Air Bridge one-to-any to be received by a user application.
Message Sequence and Length Indicators
Management Interface messages are typically single-frame messages with a payload of 0 – 4 bytes of data in addition to a Service Identifier (SID) and Data Identifier (DID). However, the Management Interface does support greater payloads across several consecutive frames with a maximum data length of 127 bytes including the SID and DID. The DLC is 8 for all messages of the Kvaser Air Bridge Management Interface.
Single and multi-framed messages can be distinguished by how the first byte of the message, the Sequence Indicator + Length (SIL), is encoded. Bit7 of single frame messages or the first frame of a multi-frame message will always be 0, indicating the frame is a new message. The remaining bits of our SIL will represent the Length of our message in bytes. The smallest possible message being 3 bytes, SIL, RSID, DID, and one byte of data, and the largest being the maximum length of 127 bytes.
For the remaining frames of a multi-frame message, bit7 of the SIL is always 1, indicating a subsequent frame of a multi-frame message, with the remaining bits indicating the remaining length of the message.