Raw Communications Packet - Intrepidcs API
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Overview

Raw communications in the intrepidcs API centers around the Raw Communication Packet (figure 1). This packet is between 4 and 18 bytes in length and has specific fields for identification and protection.

The Communication Packet

The first field of the communication packet always starts with a hexadecimal 0xAA (decimal 170). 

The next byte is the Target ID/Length Byte. In this byte, the upper nibble (the length) denotes the number of data bytes to follow not including the checksum byte *. The lower nibble of the Target ID/Length Byte includes the Target ID. The Target ID is the location for the packet on the device. For example, with the neoVI device, to send a vehicle network message on high speed CAN you would set the target id to NETID_HSCAN.  

Following the Target ID/Length byte is from 1 to 15 data bytes. 

Finally, the final byte is the checksum byte. The checksum byte is a two complement of the sum of the data bytes not including the start byte or the checksum.

* A Length of zero is not permitted but may be used in the future as an escape character

Figure 1 - The Communications Packet consists of a start identifier, a length/target byte, 1 to 15 data bytes, and a checksum.

Last Update: Monday, June 17, 2002