MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
21-36
Freescale Semiconductor
NOTE
The FRC flag is used to indicate to the CPU that the next frame can be set
up. However, it should be noted that it might be set before the DMA
controller has transferred the last byte from the eSCI to system memory. The
FRC flag should not be used if the intention is to process data. Instead, the
appropriate interrupt of the DMA controller should be used.
21.4.9.2.18 OVFL Description
The overflow (OVFL) flag is set when a byte is received in the ESCI
x
_LRR before the previous byte is
read. Because the system is responsible for reading the register before the next byte arrives, this condition
indicates a problem with CPU load. The OVFL flag is cleared by writing a 1 to the bit.
21.4.10 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 may 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 will always be generated by the LIN master.
Figure 21-23. 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.
In order 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.
21.4.10.1 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
user to decide whether the parity bits in the ID field should be calculated automatically and whether double
stop flags should be inserted after a bit error. The BRK13 bit in ESCI
x
_CR2 decides whether to generate
10 or 13 bit break characters.
Break
Sync
ID
Data
Data
CSum
...
Summary of Contents for MPC5553
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