AN2320 Freescale Semiconductor / Motorola, AN2320 Datasheet - Page 3

• Manufacturer Part Number: AN2320
• Description: Interfacing the MCF5272 to a Standalone CAN Controller
• Manufacturer: Freescale Semiconductor / Motorola

Freescale Semiconductor, Inc.
CAN Controller
with four TDM ports, a software HDLC module, a QSPI module, and support for a 3 channel PWM. In
addition, it retains the System Integration Module, the Chip-Select Module, the MAC and hardware divide
unit, the General Purpose Timers, and the real-time BDM interface standard on all ColdFire devices.
The decision to use the MCF5272 ColdFire microprocessor was based on the peripheral set, ease of
interface, and the overall system cost. There is an increasing demand for Ethernet and CAN integrated on
chip; while no ColdFire product will offer both until 2003, the MCF5272 does have on-chip Ethernet, which
reduces the additional peripherals required. There are also other MCF5272-specific peripherals, including
USB and QSPI, which may be required in industrial markets.
Also, the majority of available standalone controllers offer a multiplexed bus interface and a serial
peripheral interface (SPI); they rarely offer a non-multiplexed parallel bus interface that can be gluelessly
interfaced to a ColdFire processor. Using the MCF5272 with on-chip SPI increases the choices of suitable
CAN controllers on the market and avoids increasing the complexity and cost of the design using bus
interface glue logic.
Lastly, CAN applications, both industrial and automotive, are often cost critical; therefore, it is imperative
that overall system cost is kept to a minimum. For applications requiring both CAN and Ethernet, this
solution will still be competitively priced because of the aggressive price/performance ratio of MCF5272.
A standalone CAN solution may cost more than some 32-bit integrated solutions, but these solutions are
typically targeted at different markets and offer no Ethernet connectivity.
1.2
CAN Controller
The Infineon 82C900 TwinCAN controller is a standalone CAN controller with dual CAN nodes allowing
connection to two independent buses. It can be interfaced to a host controller using either a multiplexed bus
interface or an SPI interface, or it can be interfaced to an EEPROM via the SPI interface for initialisation
when no external host is required. The 82C900 supports up to 32 message objects which can be assigned to
both CAN nodes or one CAN node. It has a built-in, scalable FIFO mechanism for message reception and
transmission and a built-in gateway functionality for transferring messages between the nodes. There is also
a timestamp/frame counter to indicate when a message was last transmitted or received (or to indicate how
many times a message has been transmitted or received) and a CAN Analyser for monitoring activity on the
CAN bus.
There are a number of standalone CAN controller modules on the market that adhere to different
specifications, support variable data rates, and require different levels of CPU intervention. The Infineon
82C900 standalone controller was chosen because it supports the CAN 2.0B protocol, because it provides
an SPI interface for glueless connection to the MCF5272, because it will support data rates up to 1Mbit/s,
and because of the level of message transmission and acceptance filtering it supports.
There are currently three CAN protocols, CAN 2.0A, CAN 2.0B, and CAN 2.0B passive. The Infineon
device supports CAN 2.0B. The difference between these protocols lies in the length of message identifier
they can transmit and receive in a message frame. A CAN 2.0A controller can handle standard frames with
an 11-bit identifier while a CAN 2.0B controller can transmit standard frames and extended frames with
29-bit identifiers. Finally, CAN 2.0B passive controllers can transmit only standard frames but can receive
both standard and extended frames. For the majority of today’s applications CAN 2.0B is considered
standard, with system designers often requiring the extended 29-bit identifier to relieve them from
compromises with respect to defining well-structured naming schemes. The majority, if not all, of the
integrated CAN solutions on the market support CAN 2.0B. The backward-compatible nature of the CAN
protocol ensures the Infineon device can also handle messages with the standard frame format.
MOTOROLA
Interfacing the MCF5272 to a Standalone CAN Controller
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