Civil Engineering Reference
In-Depth Information
3.3
Renesas RS-CAN
As part of its most recent generation of microcontroller devices, Renesas is in-
troducing a new kind of CAN controller function. In contrast to previous im-
plementations, the RS-CAN module supports shared memory among several
channels, flexible sizes of memory areas used, and consequent assignment of
FIFO structures.
The RS-CAN module contains a proprietary CAN transfer layer from Renesas
which fulfils all the requirements of the ISO 11898, SAE J1939, and CAN 2.0B
standards.
Besides its capabilities for the full support of “Full-CAN” or “Basic-CAN” ap-
plications, there are interesting new ways the RS-CAN module can be used. Several
FIFO structures for reception and transmission allow streamed data processing, and
by combining this with the AFL (acceptance filter list), a very efficient CAN con-
troller hardware for GW applications is created.
The RS-CAN naturally also supports the conventional method of message pro-
cessing via message boxes in both the receive and transmit directions. Here, RS-
CAN can handle queued messages (with prioritized sending) concurrently.
The shared memory for all associated CAN channels allows easy transfer of
messages and signals from one channel to another. The RS-CAN hardware has a
built-in mirroring engine, which can perform this job on the message level without
any CPU interaction.
If the shared memory is used consistently, it is possible to assign individual sizes
of FIFO memories and filtering lists to the different channels, in order to tailor the
amount of memory resources available to each channel. In this way, a channel that
needs more data and filter resources can take advantage of another channel needing
less of these resources (Fig.
3.5
).
3.3.1
Properties of RS-CAN
One RS-CAN module supports up to eight CAN channels. The most popular im-
plementation includes three channels and its characteristics are described in detail
below (see Fig.
3.5
).
• CAN protocol according to ISO 11898 (2.0B active), full functionality for exten-
ded identifiers and remote frames.
• Maximum baud rate: 1 Mbit/s. This baud rate can be achieved using a module
clock at 22 MHz and a transfer layer clock at 8 MHz, if the bit timing is set to
8 tq per bit. The transfer layer clock can be derived from a separate clock source,
by using a PLL bypass, for example.
• Identical hardware structure for all derivatives and channel configurations, which
allows easy porting of software. Compatible with AUTOSAR requirements.
