MC9S12VR-Family - Data Sheet - Freescale Semiconductor

NOTE
For 20kBit/s and Fast Mode communication speeds, the corresponding slew
rate MUST be set, otherwise the communication is not guaranteed. For
10.4kBit/s, the 20kBit/s slew rate can be set but the EMC performance will
be worse. The up to 250kBit/s slew rate must be chosen ONLY for fast
mode, not for any of the 10.4kBit/s or 20kBit/s communication speeds.
15.4.2.1 10.4kBit/s and 20kBit/s
MC9S12VR Family Reference Manual, Rev. 2.8
LIN Physical Layer (S12LINPHYV1)
When the slew rate is chosen for 10.4kBit/s or 20kBit/s communication, a control loop is activated within
the module to make the rise and fall times of the LIN bus independent on VSUP and the load on the bus.
15.4.2.2 Fast Mode
Choosing this slew rate allows baud rates up to 250kBit/s by having much steeper edges (please refer to
electricals). As for the 10.4kBit/s and 20kBit/s modes, the slope control loop is also engaged. This mode
is used for fast communication only, and the LIN electricals are not supported (e.g.the LIN duty cycles).
Depending on the baud rate, a stronger external pull-up resistance might be necessary. For example, the
classical 1kΩ master resistance is enough to sustain a 100kBit/s communication. However, an external
pull-up stronger than 1kΩ might be necessary to sustain up to 250kBit/s. Which value the external
pull-up should have is let at the appreciation of the customer, depending on the baud rate. The LIN signal
(and therefore the receive LPRXD signal) might not be symmetrical for high baud rates with too high loads
on the bus.
Please note that if the bit time is smaller than the parameter t OCLIM (please refer to electricals), then no
over-current will be reported nor an over-current shutdown will occur. However, the current limitation is
always engaged in case of a failure.
15.4.3 Modes
Figure 15-10 shows the possible mode transitions depending on control bits, stop mode and error
conditions.
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