PXD20RM Datasheet, PDF (972/1628 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

27.7.4.2 Deviation error on the sync field
The deviation error is checked by comparing the current baud rate (relative to the slave oscillator) with the
received LIN sync field (relative to the master oscillator). Two checks are performed in parallel.
The first check is based on a measurement between the first falling edge and the last falling edge of the
sync field:
• If D1 > 14.84%, LHE is set.
• If D1 < 14.06%, LHE is not set.
• If 14.06% < D1 < 14.84%, LHE can be either set or reset depending on the dephasing between the
signal on LINFlexD_RX pin the f_{ipg_clock_lin} clock.
The second check is based on a measurement of time between each falling edge of the sync field:
• If D2 > 18.75%, LHE is set.
• If D2 < 15.62%, LHE is not set.
• If 15.62% < D2 < 18.75%, LHE can be either set or reset depending on the dephasing between the
signal on LINFlexD_RX pin the f_{ipg_clock_lin} clock.
Note that the LINFlexD does not need to check if the next edge occurs slower than expected. This is
covered by the check for deviation error on the full synch byte.
27.8 Test modes
The LINFlexD controller includes two test modes, Loop Back mode and Self Test mode. They can be
selected by the LBKM and SFTM bits in the LINCR1 register. These bits must be configured while
LINFlexD is in Initialization mode. After one of the two test modes has been selected, LINFlexD must be
started in Normal mode.
27.8.1 Loop Back mode
LINFlexD can be put in Loop Back mode by setting LINCR1[LBKM]. In Loop Back mode, the LINFlexD
treats its own transmitted messages as received messages. This is illustrated in Figure 27-12.
LINFlexD
Tx
Rx
LINTX
LINRX
Figure 27-12. LINFlexD in Loop Back mode
This mode is provided for self-test functions. To be independent of external events, the LIN core ignores
the LINRX signal. In this mode, the LINFlexD performs an internal feedback from its Tx output to its Rx
27-16
PXD20 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
Freescale Semiconductor