Controller Area Network (CAN) - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 647

CANCLK Tq clk

Oscillator clock
E-clock

RxCAN

MUX Prescaler

Receive/
transmit
engine

TxCAN

Control
and
status

Message
filtering
and
buffering

Tx int. req.

Configuration
registers Rx int. req.

Err. int. req.

Wake-up int. req.

Wake-
up

Low-pass
filter

Figure 13.13 ■ MSCAN12 block diagram

transceiver chip such as the MCP2551 (from Microchip) or the PCA82C250 (from Philips) to
interface with the CAN bus. In addition to providing large driving current, a CAN transceiver
chip has current protection against defected CAN or defected nodes. A typical CAN system
that includes one or more HCS12 devices is shown in Figure 13.14.

CAN node 1 CAN node 2 CAN node n

HCS12

CAN controller
(MSCAN12)

RxCAN

TxCAN

Transceiver

CAN_H CAN_L

CAN Bus

Figure 13.14 ■ A typical CAN system