MC68HC08AZ32A Datasheet, PDF (115/312 Pages) Motorola, Inc – HCMOS Microcontroller Unit

External Pins
11.3 External Pins
The MSCAN08 uses two external pins, one input (RxCAN) and one output (TxCAN). The TxCAN output
pin represents the logic level on the CAN: 0 is for a dominant state and 1 is for a recessive state.
A typical CAN system with MSCAN08 is shown in Figure 11-2.
CAN NODE 1
CAN STATION 1
CAN NODE 2
CAN NODE N
MCU
CAN CONTROLLER
(MSCAN08)
TxCAN
RxCAN
TRANSCEIVER
CAN_H
CAN_L
C A N BUS
Figure 11-2. The CAN System
Each CAN station is connected physically to the CAN bus lines through a transceiver chip. The
transceiver is capable of driving the large current needed for the CAN and has current protection against
defective CAN or defective stations.
11.4 Message Storage
MSCAN08 facilitates a sophisticated message storage system which addresses the requirements of a
broad range of network applications.
11.4.1 Background
Modern application layer software is built under two fundamental assumptions:
1. Any CAN node is able to send out a stream of scheduled messages without releasing the bus
between two messages. Such nodes will arbitrate for the bus right after sending the previous
message and will only release the bus in case of lost arbitration.
2. The internal message queue within any CAN node is organized as such that the highest priority
message will be sent out first if more than one message is ready to be sent.
MC68HC08AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
115