AN2264 Datasheet, PDF (1/20 Pages) Motorola, Inc – Freescale Semiconductor, Inc.

Application Note
AN2264/D
Rev. 0, 3/2002
LIN Node Temperature
Display
Freescale Semiconductor, Inc.
by Peter Topping
8/16 Bit Applications Engineering
Motorola, East Kilbride
Introduction
Many of the problems of excessive wiring within a car can be resolved by using
a serial multiplex bus like CAN or LIN. The LIN (Local Interconnect Network,
reference 1) bus is lower in cost and ideally suited to use within a door or in
other areas in the car where its limited data rate of 20,000 baud is adequate.
The display of external temperature is an application which falls into this
category. As a common location for the outside temperature sensor is in a wing
mirror, the data often originates from the door. The actual display is, however,
within the car some distance away and the LIN bus is eminently suitable to
facilitate the connection. A LIN node requires only 3 wires; there is one LIN data
line, the other two connections being the positive and negative supplies.
This application note presents the design of a temperature display LIN slave
node. It was developed as part of a complete door project which also included
the keypad module described in application note AN2205. The messaging
scheme for the door incorporated a byte for temperature in the mirror response
field as shown in table 1. The LIN master is, in this case, the body controller.
On a regular basis, say every 100ms, the master sends a frame header with
the mirror’s ID and it responds with the two-byte message shown. It includes a
byte with the temperature encoded in half Centigrade degree increments from
–30°C to 97.5°C. In this case the data is read directly by the temperature
display node (slave to slave communication) but could alternatively be read by
the master and retransmitted to the relevant slave node.
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© Motorola, Inc., 2002