AN2503 Freescale Semiconductor / Motorola, AN2503 Datasheet - Page 10

• Manufacturer Part Number: AN2503
• Description: Slave LIN Driver for the MC68HC908QT/QY Family
• Manufacturer: Freescale Semiconductor / Motorola

AN2503/D
Synch_Reception
State
Trimming
10
In this way, the Rx pin will be checked every bit-time. If during one of these
checks the Rx is high, the break is invalid and discarded. The desired timing
diagram for this state can be seen in
After the break is validated, the next field is the synch field. Because 0x55 is
expected, the MCU will use this field to synchronize with the master timer. If the
external oscillator is used, this process is not necessary and the program must
only wait for this byte to pass.
The trimming process is very important in LIN because it allows inexpensive
MCUs to implement LIN using an internal oscillator. Because internal
oscillators are not within an acceptable tolerance by default, they must be
trimmed to an acceptable tolerance in order to communicate properly.
This is accomplished by performing some relative calculations based on the
time elapsed between bit-times. This function is implemented as seen in
Figure
Slave LIN Driver for the MC68HC908QT/QY Family
Freescale Semiconductor, Inc.
For More Information On This Product,
6.
WAITING_NEWFRAME
InpCapt Int
Go to: www.freescale.com
INPUT CAPTURE
OVERFLOW
Figure 6. SYNCH_RECEPTION Flowchart
Figure 5. Break Timing Diagram
(RX MUST REMAIN LOW)
RECEIVING_BREAK
OV Int
GET OFFSET
START
BIT?
Figure
YES
RX = HIGH, BREAK = VALID
BREAK_BIT_COUNT Int
SYNCH_RECEPTION
5.
WRITE NEW TRIM
CALCULATE AND
3 BIT-TIMES
ELAPSED?
YES
ON_RECEPTION
INPUT CAPTURE
OVERFLOW
LAST
BIT?
YES
MOTOROLA