Specifications

Controller Area Network CAN
30
The HCAN module (Hitachi CAN)*
complies to version 2.0B (Full CAN) as
defined by Bosch.Additionally, an
independent institute has tested the
HCAN module for compliance with the
standard.CAN (Controller Area
Network) has become a widespread
standard in the European automotive
industry, because it provides very reliable,
high-speed,low-latency serial
communication for harsh and
electromagnetically polluted
environments.Therefore CAN has begun
to penetrate also industrial applications,
where these features are important.
CAN is a non-return to zero (NRZ),bit
stuffing protocol for message-orientated
serial communication via two wires,at
speeds of up to 1Mbit/s.Each message
contains up to 8 Byte of user data.Using
these short messages is important in
harsh environments, where disruption or
noise could destroy a message,as the
likelihood of such a case increases in
proportion to the length of the message.
Also, short messages keep latency low.
Depending on the actual baudrate
chosen,the length of the network can
vary between approximately 40m and
1000m (also depending on the
transceivers chosen).
CAN allows broadcasting or
multicasting,i.e.sending messages to all
or some nodes at a time, hence allows
synchronisation of the activities of several
nodes.
A key feature of CAN is the
prioritisation of messages that allows
important messages to gain access to the
physical bus with very short latency.
CAN also allow arbitration of multiple
messages that are trying to occupy the
bus simultaneously. The arbitration
mechanism will inherently grant access
to the bus for the highest priority
message.
Hitachi’s HCAN module implements the
CAN standard by adding sophisticated
features,which allows usage in even the
most demanding automotive applications
like engine management.It features:
• 15 programmable receive/transmit
buffers
• 1 receive-only buffer with local
acceptance filtering (LAFM)
• internal priority sorting to avoid
priority inversion
• flexible interrupt structure to keep
CPU load to a minimum
• sleep-mode and auto wake-up,if
CAN bus is active
• DMA support for mailbox 0 to
reduce CPU overhead
Special emphasis was put on good real
time capabilities.An internal state
machine sorts the messages by priority to
avoid the inherent priority-inversion
problem.
Peripheral address bus
Peripheral data bus
HTxD
MBI
Message buffer
HRxD
MPI
Microprocessor interface
(CDLC)
CAN
Data Link Controller
Bosch CAN 2.0Bactive
CPU interface
Control register
Status register
HCAN
Tx buffer
Rx buffer
Message control
Message data
MC0–MC15, MD0–MD15
LAFM
Mailboxes
* For a complete Roadmap of H8 microcontrollers with HCAN please refer to page 27.