MC9S12P128 Datasheet, PDF (383/564 Pages) Freescale Semiconductor, Inc – S12 Microcontrollers

11.4.5.5 LIN Transmit Collision Detection
This module allows to check for collisions on the LIN bus.
Receive Shift
Register
Synchronizer Stage
Bit Error
Compare
Bus Clock
RXD Pin
Serial Communication Interface (S12SCIV5)
LIN Physical Interface
LIN Bus
Sample
Point
Transmit Shift
Register
TXD Pin
Figure 11-18. Collision Detect Principle
If the bit error circuit is enabled (BERRM[1:0] = 0:1 or = 1:0]), the error detect circuit will compare the
transmitted and the received data stream at a point in time and flag any mismatch. The timing checks run
when transmitter is active (not idle). As soon as a mismatch between the transmitted data and the received
data is detected the following happens:
• The next bit transmitted will have a high level (TXPOL = 0) or low level (TXPOL = 1)
• The transmission is aborted and the byte in transmit buffer is discarded.
• the transmit data register empty and the transmission complete flag will be set
• The bit error interrupt flag, BERRIF, will be set.
• No further transmissions will take place until the BERRIF is cleared.
Output Transmit
Shift Register
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0
Input Receive
Shift Register
BERRM[1:0] = 0:1
BERRM[1:0] = 1:1
Compare Sample Points
Figure 11-19. Timing Diagram Bit Error Detection
If the bit error detect feature is disabled, the bit error interrupt flag is cleared.
NOTE
The RXPOL and TXPOL bit should be set the same when transmission
collision detect feature is enabled, otherwise the bit error interrupt flag may
be set incorrectly.
S12P-Family Reference Manual, Rev. 1.12
Freescale Semiconductor
383