AN1212 Freescale Semiconductor / Motorola, AN1212 Datasheet - Page 8

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

AN1212/D
Input/Output
Serial Peripheral
Interface
16-Bit Timer
JCI Overview
8
J1850 Multiplex Bus Communication Using the MC68HC705C8
and the SC371016 J1850 Communications Interface (JCI)
The MC68HC705C8 contains 24 bidirectional I/O lines, divided into three 8-bit
I/O ports, designated A, B, and C. Port D is a 7-bit input-only port, which shares
functions with the serial interface ports. The direction of the 24 I/O lines is
controlled by three data direction registers, one for each I/O port. This allows
each I/O line to be individually configured by the user as either an input or
output. The ports and data direction registers are contained in the first page of
the MCU memory map and can be read or written to directly by the user.
The MC68HC705C8 contains a serial peripheral interface (SPI) port, which can
be used for high speed serial communication with other peripherals or MCUs.
The SPI is a full-duplex, three-wire synchronous serial interface, with
programmable clock phase and polarity which can transmit data at up to
1.05 MHz (Master mode).
The MC68HC705C8 contains a timer system featuring a 16-bit free-running
counter, one programmable input capture, and one programmable output
compare. The timer can be used to record time between input transitions, or to
generate output transitions at user specified intervals. The directions for both
input edge detection and output edge generation are programmable, and a
variety of maskable CPU interrupts are available.
The SC371016 J1850 communications interface, or JCI, is an all digital device
that has been designed to handle all of the necessary communication functions
associated with transmitting and receiving frames on a J1850 compatible MUX
bus. Through the use of the proper analog transceiver, a single control input,
and the correct choice of input oscillator frequencies the JCI can be used to
transmit and receive frames in either PWM or VPW modulation, depending
upon the user’s system requirements. As mentioned above, an external analog
transceiver is required to perform the necessary analog waveshaping, output
drive, and input compare functions.
When the host MCU has a message ready for transmission onto the MUX bus,
the entire message is transmitted to the JCI, and the JCI then performs the
necessary bus acquisition, frame transmission, arbitration, and error detection
to ensure that only complete, error-free frames are transmitted. When frames
are received from the MUX bus, the JCI performs the necessary error checking,
determines if the message is of interest to that particular node and, if so,
passes the complete message to the host MCU. If desired, the JCI can transmit
its physical node address as an in-frame response during the IFR portion of the
frame.
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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