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CT 9000 ® ADV
MICROCONTROLLER
The microcontroller, U1, is an MC68HC11E2.
The powerhead
software is stored inside the microcontrollers EEPROM.
The micro-
processor uses a 4.9152 MHz crystal, X1, to generate the system
clock. This value was chosen to provide accurate baud rate times.
A power up reset and low voltage detect circuit is implemented
using U6, RN2-8 and C4.
HEATER BLANKET CONTROL
RS-422 INTERFACE
3-40
The heater blanket is powered by the +12VDC supplied by the
Power Pack.
In order for the +12VDC to be applied to the heater
blanket element, the microprocessor must turn on relay K2 and
transistor Q1.
Two thermistors located in the heater blanket provide temperature
feedback to the microcontroller.
When the injector first turns on,
the microcontroller outputs a high duty cycle PWM signal to A1. As
the desired heater blanket temperature is reached the
microcontroller will decrease the PWM duty cycle. When the heater
blanket temperature falls below the desired temperature the
microcontroller will increase the PWM duty cycle. LED DS-4 will
turn on and off with the PWM signal.
The two motor encoder channels and the microcontroller communi-
cations transmit line are input to an RS-422 transmitter, U3 pins 1,
7 and 9. These signals are then transmitted to the Power Pack.
In
addition, the RS-422 communications data transmitted from the
Power Pack to the powerhead are converted by the RS-422 re-
ceiver U5 pin 3.
800961-C
Nov. 2000
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