CAN Graphical Interface (CG) Circuit Description

WARNING: This page is about a different car, the 2010 Cadillac SRX. However, it is still accessible from the selected car via links, so may be relevant.

The CAN graphical interface (CG) is a high speed UART-based serial data interface utilizing a CAN physical layer. It is used by the Entertainment sub-system to transfer high-rate display graphics between the Radio and the Info Display Module and/or Radio/HVAC Control. In the case where the Info Display Module and Radio/HVAC Control are separate control modules, the Radio interfaces only with the Info Display Module and the Info Display Module communicates with the Radio/HVAC Control through a LIN interface. The Info Display Module therefore is responsible for passing information between the Radio and the Radio/HVAC Control. A bus wake up signal will be generated by the Radio or by the Info Display Module when the systems functionality is required. Once the CG network is awake, all message transfers on the CG are initiated by the Radio. Slave devices such as the Info Display Module and Radio/HVAC Control may not transmit unless they are responding to a request from the Radio.

Dual wire CG networks have a termination resistance between the CG+ (CAN- High) and CG- (CAN- Low) conductors at each end of the bus. Each termination resistance is 120 ohms.

The communication function of the CG shall be enabled or disabled based on the voltage level of a dedicated input (typically called "Center Stack Wake"). The network will stay awake as long as this discrete signal is driven low to less than 1.5 V. When the Radio determines that the communication bus needs to be operational or active, it shall generate the wake-up signal by pulling this signal circuit low.

The Radio can execute a warm reset of the Info Display Module if the Info Display Module fails to respond to Radio's request via the CG interface. Center Stack Reset is a low-asserted pull down output (less than 1.5 V) from the Radio to the Info Display Module and has the same electrical characteristics as those for the Center Stack Wake signal defined above.