T150/150G/T400/400G Course Computers
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Type 150/150G/400/400G Course Computers Service Manual 83156-1
Type 150/400 Course Computers
amplifier is 3.3 and the output signal RUDDER-REF x3, feeds into yet another
microcontroller ADC channel.
NMEA Inputs
The Type 150 and 400 Course Computers have two NMEA input channels, NMEA (in) 1
and NMEA (in) 2. These channels are very similar except NMEA 1 has been tuned to
work at higher baud rates for connection to P.C. RS232 serial ports (for diagnostic and
software download purposes).
Both NMEA inputs opto-isolate the incoming signal (using opto-couplers IC12 & IC14
respectively) before connecting the incoming signals to UARTs in the microcontroller.
NMEA Output
Like the NMEA inputs, there are two NMEA outputs in the Course Computers, NMEA
(out) 1 and NMEA (out) 2. Once again although very similar, NMEA 1 is tuned to work at
higher baud rates for connection to P.C. RS232 serial ports (for diagnostic purposes).
Serial data from the microcontroller’s UARTs is fed to these output circuits, which are
effectively current limited buffer stages that provide the necessary drive levels to comply
with NMEA 0183 requirements.
SeaTalk
The SeaTalk circuit is a complex bi-directional buffer stage which provides level shifting
and drive capability for both transmit and receive. This is in addition to isolation capability
in the event of fault conditions.
FET TR68 prevents the Course Computer being “back” powered from an external voltage
on the SeaTalk (Red) bus. Fuse FS2 limits the current (5 Amps) that can be supplied to
power other equipment connected to the SeaTalk bus.
When the Course Computer is not powered-up, FET TR47 isolates the transmit buffer
circuit from the SeaTalk Yellow data line. This prevents the circuit from pulling down the
data line thus preventing other equipment from communicating with each other.
FETs TR76 and TR77 provide a switching capability that enables the Course Computer to
selectively shut down either of the two SeaTalk channels in the event of a bus
communication failure, enabling the other channel to continue to function independently.
Microcontroller
The microcontroller IC15, used in the Course Computers is a NEC V850 IA1 “Phoenix”
device. This is a 32-bit architecture product with built-in Flash ROM, RAM, ADC,
Timers, UARTs and PWM outputs. The device is clocked from a 3.6864MHz crystal,
which is internally multiplied up by a factor of 10.
