AN2600 Freescale Semiconductor / Motorola, AN2600 Datasheet - Page 2

• Manufacturer Part Number: AN2600
• Description: A Simple Keypad Using LIN with the MC68HC908QT/QY MCU
• Manufacturer: Freescale Semiconductor / Motorola

AN2600/D
Main LIN Features
Application Introduction
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A Simple Keypad Using LIN with the MC68HC908QT/QY MCU
The main features of the LIN network are:
This implementation shows the usage of a 6-key keypad and one LED as an
output indicator. The MC68HC908QY/QT MCU has as many as 13
general-purpose input/output (GPIO) pins. Thus the number of application
inputs/outputs is only limited by this value and the keypad construction.
However, note that two pins are used for the LIN connectivity.
Although the communication baud rate of the LIN network is quite low (up to
20 kbps), this value is sufficient for a wide range of applications such as a
simple keypad. This particular demo application is tested for baud rates equal
to 9.6 kbps and 19.2 kbps, though Motorola LIN QY/QT driver software can be
used for any possible LIN baud rate.
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Freescale Semiconductor, Inc.
For More Information On This Product,
LIN is a single-master/multiple-slave protocol, which means that two
kinds of devices are present on the bus:
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Bus collisions are avoided because the master controls all messaging.
Therefore, there is no need for bus arbitration.
Messages are treated according to their 6-bit identifiers, similar to the
CAN standard. Thus, multicast reception is possible for broadcast type
of messages.
Only one bidirectional line of communication, allowing a communication
baud rate of up to 20 kbps. The other two connections are the positive
and negative supplies.
Variable length of data part of the frame (up to 8 bytes).
Synchronization data in every message frame, which allows low-cost
internal RC oscillators to replace crystals or ceramic resonators.
Data checksum (in LIN 2.0, this also includes ID) and bit error checking
are for data integrity. Parity bits are for ID integrity check.
Based on the common UART/SCI data encoding standard:
One dominant start bit, eight data bits (LSB first), and one recessive stop
bit. This allows easier debugging of errors and a better understanding of
the protocol.
Master — One more-powerful MCU that controls the slaves.
Slaves — Numerous (maximum number of nodes is 15) inexpensive
MCUs that have minimal features and low complexity.
Go to: www.freescale.com
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