AN1212 Freescale Semiconductor / Motorola, AN1212 Datasheet - Page 5

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

Modulation
MC68HC705C8 Microcontroller
MOTOROLA
J1850 Multiplex Bus Communication Using the MC68HC705C8
and the SC371016 J1850 Communications Interface (JCI)
In this case, the number of response bytes is limited only by the overall frame
length constraints. The third type of IFR contains data bytes, with or without a
CRC byte, from a single receiver. This type of IFR usually occurs during the IFR
portion of a frame in which that data is requested. The CRC byte, if included, is
calculated and decoded in an identical manner to the frame CRC, except the
transmitter and receiver roles are reversed. In VPW modulation, the in-frame
response byte is preceded by a normalization bit, which is required to return the
bus to the active state prior to transmitting the first bit of the IFR.
As previously mentioned, J1850 frames can be transmitted using two different
modulation techniques, pulse width modulation (PWM) or variable pulse width
modulation (VPW). The modulation technique used is dependent upon the
desired transmission bit rate and the physical makeup of the bus. The PWM
technique is primarily used with a bit rate of 41.7 kbps, and a bus consisting of
a differential twisted pair. VPW modulation is used with a bit rate of 10.4 kbps
and a single-wire bus.
For more detailed information on the features of J1850, refer to SAE
Recommended Practice J1850 – Class B Data Communication Network
Interface. Because this document is still subject to modification, the user should
ensure that the most recent revision is referenced.
The MC68HC705C8 MCU is a multipurpose HCMOS MCU based on the
industry standard M68HC05 CPU (refer to
A similar device, the MC68HC05C8, is identical to the MC68HC705C8, except
the 8K of EPROM is replaced with 8K of ROM. Some of the major features of
the MC68HC705C8 are outlined below. For a detailed description of the
features and operation of the MC68HC705C8, refer to the MC68HC705C8
Technical Data document.
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Freescale Semiconductor, Inc.
For More Information On This Product,
8K of erasable programmable read-only memory (EPROM)
176 bytes of random-access memory (RAM)
Serial peripheral interface (SPI) and serial communications interface
(SCI) interface ports
6-bit timer with one input capture and one output compare,
On-board computer operating properly (COP) watchdog system
Go to: www.freescale.com
Figure
4). It contains:
MC68HC705C8 Microcontroller
AN1212/D
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