Raymarine Autohelm ST6000, Руководство по обслуживанию

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SeaTalk Service Manual 2
1. Control Unit PCB Circuit Description
Circuit Diagram Fig. 1.
PCB Assembly/Parts List Fig. 2.
1.1 Power Supply
Incoming power is routed to the PCB via PL1 and SKT1. D4 and D20 protect against
reverse connection of the supply. IC1 is a 5V regulator and can also reset the
microprocessor, via TR1, should the supply voltage fall below approximately 6V.
1.2. Microprocessor and Program Memory
lC6 is an Intel 80C32 microprocessor. It can access up to 32k bytes of program
memory (lC5) via the latch lC4. A clock signal for the microprocessor is provided by
an 1 1MHz ceramic resonator (XL1), and associated capacitors C7 and C8.
Capacitors C6, C9 and C10 provide decoupling.
1.3. LCD and Display Driver
The LCD is a Nautech custom part. The display is driven by a Hitachi LCD driver
(IC3) deriving its drive voltages from resistor chain R24-R27 and VR1.
Communication to the microprocessor is via a 4 bit parallel bus (DB4 to DB7) and the
three control lines E, R/W and RS. Capacitors C18 and C22 provide decoupling and
resistor R44 the clock signal for lC3.
1.4. Negative Rail Generator
A negative voltage rail is required by the LCD display and is generated by a switching
regulator formed by TR11, D10 and D21. A 4.8KHz waveform is generated from the
microprocessor P3.4 (pin no. 16). This drives a charge pump, via transistorTR11,
pumping charge from C19 via D1O and C20. The negative rail is then stabilised by
D21 and R60.
1.5. N.M.E.A Interface
NMEA data is fed to the control unit via PL2 and isolated from the rest of the circuit
using the opto-isolator (lC7). Diode D1 provides input reverse connection protection
and resistor R35 is tuned to give the desired bandwidth of operation. The output from
IC7 is connected to the microprocessor Port P3.2 (pin 14). Capacitor C21 provides
decoupling.
1.6. SeaTalk Bus Transmit and Receive
SeaTalk transmit and receive circuitry consists of TR5, 6, 7, 8, 9, 14 and 15 and their
associated components. Data transmission is at 4800 band with a low start bit and
line idling high. TR7 and TR8 provide high and low drive respectively, whilst TR14
and R57 give overload protection to TR8 in the event of misconnection. TR5 and TR6
allow the microprocessor to monitor its own transmissions and also to receive data
from other units on the bus.