Simrad TP10 Service Manual page 18

SIMRAD
Issue 4.0 17/09/03
Microprocessor Reset. Integrated Circuit IC6 is an integrated reset generator for the
microprocessor which produces a reset LOW pulse of approximately 50mS duration at switch on
and whenever a 5v supply failure occurs. In addition to the reset provided by IC6, the
microprocessor has a built in watchdog timer which will create a reset if a software crash occurs for
any reason.
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Non-Volatile Memory (NVM). Integrated Circuit IC3 provides 1Kbit of E memory for the retention
of important data after power down.
Fluxgate (Compass). Two anti-phase signals are provided from microprocessor Ports P1.7 and
P1.6. These signals are buffered by TR15 and TR16 to provide a higher current drive to the
excitation coil of the fluxgate. A reference voltage level of +2 volts is provided by R46 and R53
decoupled by C53. The 2 coils, mounted at right angles, provide output signals proportional to the
sine and cosine of the Earth's magnetic field. These signals are fed via the electronic switch IC9,
to 2 dual slope integrating analogue to digital converters IC7 and IC 8 plus associated
components. The outputs of the comparator IC7 are fed to the microprocessor Ports P1.4 and
P1.5 which provide input capture facilities. Accurate timing of the conversion is kept by the
microprocessor to provide simultaneous precision analogue to digital conversion of both sine and
cosine signals to avoid errors created by multiplexing the inputs.
Motor Drive. The motor drive signals (MDRIVE_A and MDRIVE_B) are generated from the
microprocessor at Ports P0.7 and P0.6, these lines being LOW when there is no drive and HIGH to
drive. The drive outputs control IC10 and IC11 which are comparators set at threshold levels of
+4V and +1V produced by the resistor network R71, R72 and R73. The comparators invert the
signals and provide the current to switch the MOSFETs in stages which prevents both P and N
channel MOSFETs on the same side of the "H-bridge" configuration, (i.e. TR10 and TR11 or TR12
and TR13), being partially switched on at the same time. When there is no drive, both N-channel
MOSFETs TR11 and TR13 are switched on giving a direct short across the motor to the 0V line
thus providing active braking
EMC. Capacitors with values of 100pF, 100nF and 1nF are extensively used to decouple noise
from switched data lines. Two A.C. coupled connections labelled "CHASSIS" , routed via
capacitors C63 and C64, were provided for interconnection to the internal metalwork for EMC
purposes. Tests have confirmed that connection is not required.
Hall Effect PCB.
Introduction. The Hall Effect PCB is a generic item which can be used for both Tillerpilots TP10,
TP20 and TP30 and Wheelpilots WP10 and WP30. For Tillerpilots, the Hall Effect devices are
mounted vertically into the PCB and horizontally for Wheelpilots. The circuit diagram for the Hall
Effect PCB is given in Drawing No. E03182.
Feedback. Two Hall Effect sensors HE1 and HE2 are mounted on the Hall Effect PCB and sense
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the rotation of 2 small bar magnets mounted 180 apart in the pulley wheel. This produces a
quadrature feedback output, at logic levels, FB1 and FB2. The PCB is powered from the host unit
+5V regulated supply, the line being filtered by C1, and signals FB1 and FB2 are fed back to the
microprocessor via pull-up resistors on the host unit PCB.
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