MC908AS60ACFU Datasheet, PDF (268/414 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

MSCAN Controller (MSCAN08)
23.3 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 23-1.
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 23-1. 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
defected CAN or defected stations.
23.4 Message Storage
MSCAN08 facilitates a sophisticated message storage system which addresses the requirements of a
broad range of network applications.
23.4.1 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.
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
268
Freescale Semiconductor