MC68HC08AZ16 Datasheet, PDF (352/527 Pages) Motorola, Inc – HCMOS Microcontroller Unit

msCAN08 Controller (msCAN08)
Message storage
Each CAN station is physically connected 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.
Message storage
msCAN08 facilitates a sophisticated message storage system which
addresses the requirements of a broad range of network applications.
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.
Above behaviour can not be achieved with a single transmit buffer. That
buffer must be reloaded right after the previous message has been sent.
This loading process lasts a definite amount of time and has to be
completed within the Inter-Frame Sequence (IFS) in order to be able to
send an uninterrupted stream of messages. Even if this is feasible for
limited CAN bus speeds it requires that the CPU reacts with short
latencies to the transmit interrupt.
A double buffer scheme would de-couple the re-loading of the transmit
buffers from the actual message sending and as such reduces the
reactiveness requirements on the CPU. Problems may arise if the
sending of a message would be finished just while the CPU re-loads the
second buffer, no buffer would then be ready for transmission and the
bus would be released.
5-can
MOTOROLA
msCAN08 Controller (msCAN08)
MC68HC08AZ32
351