Enhanced Serial Communication Interface (eSCI)
MPC5565 Microcontroller Reference Manual, Rev. 1.0
Freescale Semiconductor
20-37
20.4.10 Using the LIN Hardware
The eSCI provides special support for the LIN protocol. It can be used to automate most tasks of a LIN
master. In conjunction with the DMA interface it is possible to transmit entire frames (or sequences of
frames) and receive data from LIN slaves without any CPU intervention. There is no special support for
LIN slave mode. If required, LIN slave mode can be implemented in software.
A LIN frame consists of a break character (10 or 13 bits), a sync field, an ID field,
n
data fields (
n
could
be 0) and a checksum field. The data and checksum bytes are either provided by the LIN master (TX frame)
or by the LIN slave (RX frame). The header fields are always generated by the LIN master.
Figure 20-23. Typical LIN frame
The LIN hardware is highly configurable. This configurability allows the eSCI’s LIN hardware to generate
frames for LIN slaves from all revisions of the LIN standard. The settings are adjusted according to the
capabilities of the slave device.
To activate the LIN hardware, the LIN mode bit in the ESCI
x
_LCR needs to be set. Other settings, such
as double stop flags after bit errors and automatic parity bit generation, are also available for use in LIN
mode.
The eSCI settings must be made according to the LIN specification. The eSCI must be configured for
2-wire operation (2 wires connected to the LIN transceiver) with 8 data bytes and no parity. Normally a
13-bit break is used, but the eSCI can also be configured for 10-bit breaks as required by the application.
20.4.10.1 Features of the LIN Hardware
The eSCI’s LIN hardware has several features to support different revisions of the LIN slaves. The
ESCI
x
_LTR can be configured to include or not include header bits in the checksum on a frame by frame
basis. This feature supports LIN slaves with different LIN revisions. The LIN control register allows the
application to automatically calculate the parity bits in the ID field and insert double stop flags a bit error.
The BRK13 bit in ESCI
x
_CR2 decides whether to generate 10 or 13 bit break characters.
NOTE
LIN 2.0 requires a 13-bit break character. Set the BRK13 bit to 1. The eSCI
bus works when BRK13 = 0, but the setting does not comply with LIN 2.0.
The application software can disable checksum generation/verification for individual frames to perform
the functions externally and use the LIN hardware to append two CRC bytes (
). Although the
LIN standard does not include CRCs, CRCs are processed as data bytes by the LIN protocol. CRCs are
used in software applications that process very large frames. The eSCI and FlexCAN modules use the same
CRC polynomial, the LIN protocol processes CAN bytes as data bytes.
Figure 20-24. LIN Frame with CRC bytes
Break
Sync
ID
Data
Data
CSum
...
Break
Sync
ID
Data
Data
CRC1
CRC2
CSum
• • •
Содержание MPC5565
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