Hacking Cars: Protocols


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We’ve gone over the basics of CAN and looked into how CAN databases work. Now we will look at a few protocols that are commonly used over CAN.

In the last article we looked at CAN databases, where each bit of a message is mapped to a specific meaning. For example, bit 1 of a CAN message with ID 0x400 might represent whether the engine is currently running or not.

can-hacking-part-2

However, for more complex communications we need to use protocols. These can map many meanings to a single CAN ID by agreeing on a structure for sending and receiving data.

OBD-II

The standard OBD-II connector
The standard OBD-II connector

Next time you’re in the drivers seat, look around your left knee. You’ll find a connector like the one above. This is the OBD-II connector.

The OBD-II protocol is not CAN specific, and can be implemented over UART and PWM channels as well as CAN…

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