|
MC912D60AVPVE8 Datasheet, PDF (295/460 Pages) Freescale Semiconductor, Inc – HC12 Microcontrollers | |||
|
◁ |
Freescale Interconnect Bus
Interfacing to MI Bus
VDD
TX
4.7 kâ¦
MCU
RX
VSS
10 kâ¦
+12 V
18 V
3.9 kâ¦
VDD
10 kâ¦
22 kâ¦
VDD
1.2 kâ¦
T1
MI Bus
Figure 16-4. A typical MI Bus interface
The transistor serves both to drive the MI Bus during the push field and
to protect the MCU TX pin from voltage transients generated in the
wiring. Without the transistor, EMI could damage the TX pin. Similarly,
the input pin (RX) is protected from EMI by clamping it to the MCU supply
rails with two diodes. When a load dump occurs, the zener diode (18V)
is switched on and hence turns the transistor on; this generates the logic
â0â state on the MI Bus. After eight time slots (200ms) of continuous â0â
state, all devices on the MI Bus will have their outputs disabled.
The MI Bus line can take two states, recessive or dominant. The
dominant state (â0â) is represented by a maximum 0.3V (VCESAT of the
transistor, T1). The recessive state (â1â) is represented by 5V, through a
pull-up resistor of 10kâ¦.
The bus load depends on the number of devices on the bus. Each device
has a pull-up resistor of 10kâ¦. An external termination resistor is used
to stabilize the load resistance of the bus at 600â¦.
MC68HC912D60A â Rev. 3.1
Freescale Semiconductor
Freescale Interconnect Bus
Technical Data
295
|
▷ |