AN1212 Freescale Semiconductor / Motorola, AN1212 Datasheet - Page 15

• Manufacturer Part Number: AN1212
• Description: J1850 Multiplex Bus Communication Using the MC68HC705C8 and the SC371016 J1850 Communications Interface (JCI)
• Manufacturer: Freescale Semiconductor / Motorola

Message
Transmitter
and Receiver
MC68HC705C8/JCI Interface Driver Routines
MOTOROLA
J1850 Multiplex Bus Communication Using the MC68HC705C8
and the SC371016 J1850 Communications Interface (JCI)
JCI will discard the message, and inform the host MCU that a transmission
error has occurred. Loss of arbitration is not considered a transmission error.
For more information on the different methods of error detection and
notification used by the JCI, refer to J1850 Communications Interface
Specification, Chapter 4: MCU Interface and Chapter 7: MUX Interface.
As mentioned above, the JCI is an all digital device and requires an analog
transceiver to supply all transmit waveshaping, transmit drive, and input
compare functions. The JCI transmits the frame to the physical interface at
digital CMOS levels, where the appropriate waveshaping and drive takes
place. Frames being received from the MUX bus are converted back to digital
CMOS levels by the analog physical interface and then transmitted to the JCI,
where physical interface rise/fall times and propagation delays are taken into
account.
For more information on transmitting and receiving messages and transceiver
interfacing, refer to J1850 Communications Interface Specification, Chapter 7:
MUX Interface.
Communication on the J1850 MUX bus using the JCI can be subdivided into
three basic tasks: setup, transmitting, and receiving.
Setup includes:
Transmitting involves:
Receiving involves:
These basic driver routines have been divided into these three sections, which
should allow the to be more easily understood and used. Each section is
detailed below.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Hardware configuration
Host MCU initialization
JCI reset
Loading the ACR and AMR registers with the appropriate message filter
data
Assembling the necessary message bytes
Transferring the message bytes to the JCI
Monitoring the JCI to determine when the message has been
transmitted successfully
Retrieving message data from the JCI
Doing any additional filtering
Storing the data where the user’s application software can
access it.
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MC68HC705C8/JCI Interface Driver Routines
AN1212/D
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