B&B Electronics HVD100A3 Intelligent Mode Command Protocol, Intelligent Mode Message Structure

Intelligent Mode Command Protocol

The HDV100A3 uses a simple protocol to communicate to vehicle bus. The protocol is divided into four parts:

Start Of Frame (SOF)

Control Field (shown in light gray) Data Field (shown in dark gray) Checksum (CS)

Intelligent Mode Message Structure

SOF	Number of	Control Bytes	Number of
	Control Bytes		Data Bytes
1 byte	1 byte	1 to 20 bytes	1 byte

Data Bytes

1 to 100 bytes

CS

1 byte

The Start of Frame byte is the first byte in a valid frame and is always 01 hex.

The Control Field sets up the function and control of the HDV100A3 hardware and is formatted as shown below.

Control Field Structure

Number of Control	ID Byte	Function	Control Data Bytes
Bytes to Follow		Byte
1 byte	1 byte	1 byte	Up to 20 bytes

The first byte of the Control Field is the number of control bytes in the message. This value indicates the number of control bytes, excluding itself, to follow. If the message doesn’t contain any control bytes, the Number of Control Bytes value will be set to 00 hex as a placeholder.

The next part of the message frame is the data field. The data field is preceded by the number of data bytes, excluding itself, to follow and is set to 00 hex if no data is present in the message. The data field is reserved for data that is to be communicated to the vehicle bus.

Data Field Structure

Number of	Data Bytes
Data Bytes
1 byte	Up to 100 bytes

The last element of a valid message is the checksum. The checksum is calculated by adding ALL bytes from the Start of Frame (inclusive) to the last data byte and using the last 8 bits as a checksum.

2	HDV100A3 Command & Response Manual-1306cr
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