AN2633 Freescale Semiconductor / Motorola, AN2633 Datasheet - Page 4

• Manufacturer Part Number: AN2633
• Description: LIN Drivers for SLIC Module on the MC68HC908QL4
• Manufacturer: Freescale Semiconductor / Motorola

AN2633/D
High-Speed
Communications and
Factory Programming
Smaller, Faster
Driver Code
Fewer Interrupts to
Service
4
The SLIC is also capable of high-speed operations without the need to change
driver code. It will automatically synchronize to LIN messages, up to 120 kbps
(depending on CPU speed and filter settings). This is especially useful for
downloading code in a factory programming environment.
To accommodate higher speed messages, changes may be required to
ensure:
Automation of many standard LIN communication functions allows for much
smaller and more efficient driver code, which frees up vital CPU and memory
resources. Smaller driver code means that devices with less memory can be
used in some applications. Applications that require a 4K FLASH when using
an ESCI or timer module might easily fit in a 2K FLASH device if using the SLIC
module. Even in a 2K FLASH device (such as HC908QL2), more than 90% of
the FLASH memory is available for the application to use.
Many applications, especially motor control systems, often have stringent
timing requirements to maintain adequate control.
To service the LIN communications, the SLIC module requires a maximum of
two interrupts for any standard LIN message frame (1 to 8 data bytes). If a
message header that the application does not need to handle arrives, the SLIC
module would require only one interrupt.
Compared to a UART-based solution, this reduction in interrupts can mean
eliminating as many as 10 interrupts per message frame.
interrupts required for servicing an 8-byte LIN request frame using both the
SLIC module and a traditional UART-based solution. Channel 1 (third trace
from top) of the scope capture shows the ISR firing on the SLIC module (two
interrupts required). Channel 4 (fourth trace from top — inverted polarity)
shows that 12 interrupts are required to service the same message with a
UART-based controller.
LIN Drivers for SLIC Module on the MC68HC908QL4
•
•
Freescale Semiconductor, Inc.
For More Information On This Product,
that the digital receive filter is adjusted, which prevents filtering out valid
high-speed data
that the physical layer device (such as a MC33661 enhanced LIN
transceiver) slew rate control is adjusted to prevent attenuating the bits
of the high speed message
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Figure 2
MOTOROLA
shows the