參數(shù)資料
型號: MC68HC05X4CDW
廠商: MOTOROLA INC
元件分類: 微控制器/微處理器
英文描述: HCMOS Microcontroller Unit
中文描述: 8-BIT, MROM, 2.2 MHz, MICROCONTROLLER, PDSO28
封裝: PLASTIC, SOIC-28
文件頁數(shù): 98/156頁
文件大小: 926K
代理商: MC68HC05X4CDW
Motorola CAN
MC68HC05X4
98
Motorola CAN
MOTOROLA
Interface to the MCAN bus
Physically, the MCAN bus may be composed of two wires. The bus can
take on one of two values: dominant or recessive. During simultaneous
transmission of dominant and recessive bits by two or more CAN
modules the resulting bus value will be dominant. (For example, with a
wired-AND implementation of the bus, the dominant level would
correspond to a logic 0, and the recessive level to a logic 1.)
The two wires of the MCAN bus are designated CANH and CANL. The
voltage levels appearing on these lines are designated V
CANH
and V
CANL
.
A simple termination network is required for each wire.
Figure 21
shows
the physical interface circuitry within the MCAN module, and its
connection to the MCAN bus with a typical low speed (<125 kbaud)
hardware interface. (Note that the suggested values shown in the
diagram are subject to change in the future.)
For the voltage and resistor values shown in
Figure 21
the voltages on
the MCAN bus are:
Recessive level:
V
CANH
= 3.25 V
V
CANL
= 1.75 V
Dominant level:
V
CANH
= 1.00 V
V
CANL
= 4.00 V
If several CAN modules are driving a dominant level on the bus at the
same time then the values for V
CANH
and V
CANL
can go to 0.3 and 4.7 volts
respectively. The residual 0.3 V is due to the voltage drop across the
diodes and driver transistors in the transmission circuit.
The receiver part of the network uses two identical voltage divider
networks, with a divide ratio of 6:1 (resistor values of 150k
and 30k
)
referenced to V
DD
/2. This increases the common mode range of the input
comparator on the physical bus lines. If the common mode range of the
comparator at its inputs is 1.5 to 3.5 volts then, for V
DD
= 5.0 V, the
common mode range will be increased to –3.5 to +8.5 volts on the bus
lines.
30-mcan
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.
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