Chapter 23 LIN Physical Layer (S12LINPHYV2)
S12ZVHY/S12ZVHL Family Reference Manual Rev. 1.05
Freescale Semiconductor
765
23.4
Functional Description
23.4.1
General
The LIN Physical Layer module implements the physical layer of the LIN interface. This physical layer
can be driven by the SCI (Serial Communication Interface) module or directly through the LPDR register.
23.4.2
Slew Rate and LIN Mode Selection
The slew rate can be selected for Electromagnetic Compatibility (EMC) optimized operation at 10.4 kbit/s
and 20 kbit/s as well as at fast baud rate (up to 250 kbit/s) for test and programming. The slew rate can be
chosen with the bits LPSLR[1:0] in the LIN Slew Rate Mode Register (LPSLRM). The default slew rate
corresponds to 20 kbit/s.
The LIN Physical Layer can also be configured to be used for non-LIN applications (for example, to
transmit a PWM pulse) by disabling the TxD-dominant timeout (LPDTDIS=1).
Changing the slew rate (LPSLRM Register) during transmission is not allowed in order to avoid unwanted
effects. To change the register, the LIN Physical Layer must first be disabled (LPE=0). Once it is updated
the LIN Physical Layer can be enabled again.
NOTE
For 20 kbit/s and Fast Mode communication speeds, the corresponding slew
rate
MUST
be set; otherwise, the communication is not guaranteed
(violation of the specified LIN duty cycles). For 10.4 kbit/s, the 20 kbit/s
slew rate
can
be set but the EMC performance is worse. The up to 250 kbit/s
slew rate must be chosen
ONLY
for fast mode, not for any of the 10.4 kbit/s
or 20 kbit/s LIN compliant communication speeds.
23.4.2.1
10.4 kbit/s and 20 kbit/s
When the slew rate is chosen for 10.4 kbit/s or 20 kbit/s communication, a control loop is activated within
the module to make the rise and fall times of the LIN bus independent from VLINSUP and the load on the
bus.
23.4.2.2
Fast Mode (not LIN compliant)
Choosing this slew rate allows baud rates up to 250 kbit/s by having much steeper edges (please refer to
electricals). As for the 10.4 kbit/s and 20 kbit/s modes, the slope control loop is also engaged. This mode
is used for fast communication only, and the LIN electricals are not supported (for example, the LIN duty
cycles).
A stronger external pullup resistor might be necessary to sustain communication speeds up to
250 kbit/s.
The LIN signal (and therefore the receive LPRxD signal) might not be symmetrical for high
baud rates with high loads on the bus.
