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SeaTalk Service Manual
2
1. ST 6000 Course Computer Circuit Description
Circuit diagram Fig. 1.
PCB Assembly/Parts List Fig. 2
1.1 Power Supply
Incoming power is routed to the PCB. via the 'D' connector socket SKI. VI provides
suppression against any voltage spikes present on the incoming DC supply whilst
D15 protects against accidental reverse connection of the supply. 1C 1 is a 5v
regulator with an integral reset function which resets the microprocessor, via Tr9,
should the supply voltage be insufficient to maintain regulation.
1.2 Microprocessor and Program memory
IC2 is an Intel 80C32 microprocessor with 256 bytes of on board Ram. It can
access up to 32K bytes of programme memory in IC7, via the latch IC6.
A Clock Signal for the microprocessor is provided by an 11MHz ceramic resonator
(XL1) and C15 & C16. Alternatively. XL2 can be used which combines all three
components in one package.
1.3 Power Amplifier
TR23, 24, 25 and TR26 are configured to form a power amplifier capable of driving
a motor in four modes:-
1. Drive right
2. Drive left
3. Short circuit motor (Brakes Motor)
4. Open circuit motor
Mode 3 is used to stop the motor quickly by switching Tr23 and 25 On and TR24
and 26 Off. Mode 4 allows the motor speed to be measured by switching off all of
the power transistors.
All four modes are controlled via pins 8 and 9 of the microprocessor IC2.
1.4 Analogue to digital Converter
IC3.4 and 9 form a software driven analogue to digital Converter. IC3 and 9 are 8
channel multiplexed analogue switches routing all analogue signals, (see table
below), through to IC4 which is configured as an integrator. C9 is discharged at a
constant rate triggering the comparator IC5 as it reaches a level of approximately
0.53v. The output of the comparator is connected to the microprocessor allowing
measurement of the discharge time which is directly proportional to the analogue
input. Analogue channels:-
IC3 Channel 0 Reset integrator
Channel 1 Integrator discharge signal
Channel 2 Fluxgate sense A
Channel 3 Fluxgate sense B
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