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PDF AN2633 Data sheet ( Hoja de datos )
| Número de pieza | AN2633 | |
| Descripción | LIN Drivers Application Note | |
| Fabricantes | Motorola Semiconductors | |
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Application Note
AN2633/D
Rev. 1, 3/2004
LIN Drivers for SLIC Module
on the MC68HC908QL4
Freescale Semiconductor, Inc.
By: Matt Ruff
8/16 Bit Systems Engineering
Austin, Texas
Overview
This application note describes three versions of a slave LIN driver developed
for the slave LIN interface controller (SLIC) module on the MC68HC908QL4
(QL4) microcontroller unit (MCU). The slave driver comes with the Motorola
QL4 LIN kit evaluation board, which also contains AN2573/D: LIN Kits LIN
Evaluating Boards, which demonstrates the functionality of the driver.
The slave driver also comes with the M68EVBQL4 evaluation board (EVB)
from Metrowerks, along with a compatible version of the application code for
the EVB. The software for the LIN kit, including this driver, can be downloaded
from the Motorola LIN website: http://motorola.com/semiconductors/LIN
Local Interconnect
Network (LIN)
LIN (local interconnect network) is a low-cost communication protocol often
used in automotive applications that do not require the bandwidth and
versatility of CAN. The LIN bus uses only a single data wire and can
communicate at speeds up to 20 kbps. A LIN network has a single master and
multiple slaves, so bus arbitration is not required.
The driver and application was developed from the LIN Specification Package.
(See References for this and other useful resources.)
NOTE:
With the exception of mask set errata documents, if any other Motorola
document contains information that conflicts with the information in the device
data sheet, the data sheet should be considered to have the most current and
correct data.
Cyclone® and MultiLink® are registered trademarks of P&E Microcomputer Systems, Inc.
This product incorporates SuperFlash® technology licensed from SST.
© Freescale Semiconductor, Inc., 2004. All rights reserved.
For More Information On This Product,
Go to: www.freescale.com
© Motorola, Inc., 2004
Free Datasheet http://www.Datasheet4U.com
1 page  
Freescale Semiconductor, Inc.
AN2633/D
SLIC Module Operation, Features, and Benefits
Figure 2. SLIC versus UART-Based Interrupt Handling
With 10 fewer interrupts to service (an 83.3% reduction in interrupts), the CPU
is free for a much greater amount of time. Using the SLIC module instead of a
UART-based solution significantly reduces the chance of an interrupt
interfering with other application operations.
Faster, More Efficient
Interrupt Servicing
In addition to reducing the number of interrupts required to service a LIN frame
(two interrupts only), the SLIC module has been designed to maximize the
efficiency of the interrupt service routine (ISR), which minimizes the CPU
requirements for LIN communications. A patented encoding method is used to
allow the ISR to service all SLIC interrupts in a short, fixed, and predictable
amount of time. Details of this are explained in CodeWarrior Project —
Assembly Source Code Basic SLIC Driver.
Because the SLIC module automates standard LIN communication functions,
less time is spent inside the ISR. Checksum calculations have been
automated, which eliminates the extra instructions that would be needed to
perform this calculation in a UART solution. This further reduces the amount of
LIN Drivers for SLIC Module on the MC68HC908QL4
For More Information On This Product,
Go to: www.freescale.com
5
Free Datasheet http://www.Datasheet4U.com
5 Page 
Freescale Semiconductor, Inc.
AN2633/D
CodeWarrior Project — Assembly Source Code Basic SLIC Driver
in the main() routine. This monitors LINSleep flag and sets power states
accordingly. Due to differences in hardware between the EVB and LIN kit
board, this routine only turns off the LEDs to indicate the sleep mode condition.
In actual applications, it is likely the designer would power down the node for
sleep mode for energy conservation.
Exact procedures for putting the SLIC to sleep and waking it up again are
beyond the scope of this note, but it is important to remember a few basic
concepts. Like many communication peripheral modules, the SLIC contains a
state machine that synchronizes to the LIN message traffic. It is important to
safely disable the SLIC by writing the INITREQ bit before turning off the
physical layer. Doing this will avoid confusing the state machine and inducing
potentially undesirable side effects.
Depending on external circuitry, turning off the physical layer device can have
different effects on the rest of the system. On the LIN kit board, for example,
disabling the physical layer will activate the inhibit function (INH pin) on the
voltage regulator and power down the MCU. LIN bus activity will then restore
power to the MCU and the code will go through a POR.
On the EVB, however, the INH pin of the physical layer is not connected to the
regulator at all. Turning off the physical layer on the EVB will result in the Rx
line to the SLIC being driven to a low state. The SLIC should be disabled first,
to prevent it from trying to interpret this as a break symbol. Do NOT try to
disable the SLIC from within the SLIC ISR. Disable the SLIC only in a code
location outside the ISR such as the Check_LIN_Sleep() routine, where the
LINSleep flag is recognized and before the physical layer is disabled.
CodeWarrior Project — Assembly Source Code Basic SLIC Driver
The first project described shows a basic C-based LIN slave application with a
SLIC ISR written in assembly code. Writing the ISR in assembly allows the
greatest degree of control over the performance and the size of the final code.
In very small embedded systems, such as those used in LIN slave nodes, code
size and performance efficiency are critical to getting the most out of very few
resources.
One of the key features of handling the ISR in assembly code is to use the
design of the SLIC module to ensure maximum execution efficiency. The SLIC
state vector register (SLCSV) is encoded to allow the user to build a jump table.
When using a jump table, no matter what interrupt source is being serviced, the
ISR will begin servicing the interrupt in a fixed amount of time.
The SLCSV register value is loaded into the index register, then used as an
offset into the jump table. The entries in the jump table point to service handler
LIN Drivers for SLIC Module on the MC68HC908QL4
For More Information On This Product,
Go to: www.freescale.com
11
Free Datasheet http://www.Datasheet4U.com
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet AN2633.PDF ] | |
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