PXS20RM Datasheet, PDF (982/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

LIN Controller (LINFlexD)
• The classic checksum sums all data bytes, and is used for communication with LIN 1.3 slaves.
• The enhanced checksum sums all data bytes and the identifier, and is used for communication with
LIN 2.0 (or later) slaves.
31.4 LINFlexD and software intervention
The increasing number of communication peripherals embedded on microcontrollers (for example, CAN,
LIN, SPI) requires more and more CPU resources for the communication management. Even a 32-bit
microcontroller is overloaded if its peripherals do not provide high level features to autonomously handle
the communication.
Even though the LIN protocol with a maximum baud rate of 20 Kbit/s is relatively slow, it still generates
a non-negligible load on the CPU if the LIN is implemented on a standard UART, as is usually the case.
To minimize the CPU load in Master mode, LINFlexD handles the LIN messages autonomously.
In Master mode, once the software has triggered the header transmission, LINFlexD does not request any
software (that is, application) intervention until the next header transmission request in transmission mode
or until the checksum reception in reception mode.
To minimize the CPU load in Slave mode, LINFlexD requires software intervention only to:
• Trigger transmission or reception or data discard depending on the identifier
• Write data into the buffer (transmission mode) or read data from the buffer (reception mode) after
checksum reception
If filter mode is activated for Slave mode, LINFlexD requires software intervention only to write data into
the buffer (transmission mode) or read data from the buffer (reception mode)
The software uses the control, status and configuration registers to:
• Configure LIN parameters (for example, baud rate or mode)
• Request transmissions
• Handle receptions
• Manage interrupts
• Configure LIN error and timeout detection
• Process diagnostic information
The message buffer stores transmitted or received LIN frames.
31.5 Summary of operating modes
The LINFlexD controller has three operating modes:
• Normal
• Initialization
• Sleep
After a hardware reset, the LINFlexD controller is in Sleep mode to reduce power consumption.
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PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor