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| Freescale 汽车CAN解决方案 |
| 作者： 时间：2008-08-27 来源:eaw |
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Freescale 汽车CAN解决方案:
The controller area network (CAN) is a serial, asynchronous, multi-master communication protocol for connecting electronic control modules in automotive and industrial applications. CAN was designed for automotive applications needing high levels of data integrity and data rates of up to 1 Mbit/s. Freescale Semiconductor has a complete line of products to enable automotive electronics designers to incorporate CAN into their applications.
Different CAN Implementations to Meet Different CAN Performance Needs
Freescale recognizes the challenges that face designers of automotive CAN devices and systems. Because different CAN networks have different CAN messaging needs, Freescale provides different CAN hardware options to meet these challenges.
Freescale’s 32-bit microcontrollers use either the TouCAN or FlexCAN hardware modules to communicate on the CAN bus. These modules are based on the traditional mailbox or “full-CAN” hardware architecture that provides 16 message buffers. When messages are received, a hardware filter match will drop the message into one of the ‘mailboxes’ (receive buffers). This approach works very well with powertrain systems, where messages are very regular and predictable, as the application designer can ensure that the software empties the mailboxes fast enough to keep new messages from over-writing the old messages in the boxes. If the boxes are not emptied fast enough because multiple messages come in too quickly with the same identifier, data can be lost. This is why mailbox architectures are not always suited to networks with unpredictable, event-driven data.
As stated before, body electronics networks have messaging that can be very sporadic and unpredictable in nature, which makes the Freescale Scalable CAN (msCAN) architecture so well suited to these applications. Since HC08, HC12, and HCS12 microcontroller families are 8-bit and 16-bit microcontrollers which are the backbone of body electronics systems and components, the msCAN module is a perfect fit for these families. CAN messages received by msCAN are placed into a single first-in, first-out (FIFO) storage structure. This structure maintains the order of received messages and allows many messages with identical identifiers to be received in rapid succession without concern of overflow of a single receive buffer.
Freescale SMOS CAN Physical Layer Products to Meet Automotive Customer Needs
To address the need for multiple types of CAN physical layers, Freescale offers a range of CAN physical layer devices designed to meet or exceed the performance standards set out by ISO and SAE.
But a simple physical layer device is not always enough. For example, all automotive modules need to run from a regulated power supply. Sometimes a local switch or sensor might need to wake up the module from sleep state to active running state very quickly. That switch or sensor might be running at vehicle battery levels. This is where the Freescale System Basis Chip (SBC) brings power and value to the automotive design table. SBCs combine the CAN physical layers needed for automotive CAN connectivity with voltage regulation, independent watchdog timer, and local wake-up circuitry to allow greater flexibility with fewer components. Since these circuits can be made with the same semiconductor processes, it makes sense to combine these functions into one package and reduce the number of components needed in the final design. This reduces assembly costs, increases reliability, and increases design flexibility.
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