Sailor RM2042 Technical Manual page 58

5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS
UNBALANCED TX AF AMPLIFIER
As mentioned above the unbalanced output has to be used, if RM2042 is connected to RT2047 or
RT2048. The input signal to the unbalanced TX AF amplifier is attenuated and buffered by the operational
amplifier U3.3. The output level is adjustable from -30dBm to -10dBm and is controlled by the trimming
potentiometer R22.
12V/24V WIRING CIRCUIT
The RM2042 can be supplied from two different sources, which are:
12V battery
SAILOR power supply, N420 or N418 (24V to 12V)
To select the wanted power source, the interface module is mounted with a strap field, which is accessible
from the rear panel. How to code this strap field is shown in chapter 2, which deal with the installation of
RM2042.
5V POWER SUPPLY
The interface module include two separate 5V serial regulators. The one, U5, is only used to supply the
loudspeaker amplifier and this voltage is designated +5VA in the diagram. The other one, U1, is used to
supply all digital circuits at the interface, microprocessor and display modules. This regulator is
constructed with an energy reservoir at its input terminal. The energy reservoir is realized by a 1000F
capacitor (C3). This capacitor is able to hold the regulator output constantly at 5V for a periode of about
20msecs, even if the supply voltage is completely removed. This time periode is sufficient for the
microprocessor to succeed the saving of all importen data. The hold function of the 5V supply voltage is
included to handle situations, where RM2042 is turned off or the power supply voltage is removed
because of a failure. The diode D1 is used to avoid immediate discharging of C3, if the input power supply
voltage is grounded in a failure situation.
POWER FAILURE RESET CIRCUIT
The power failure reset circuit is included to handle those cases, where the input power supply voltage
shortly drops out. Such a power failure will immediately be detected by the microprocessor by means of
an error signal, which is generated by the 10V voltage regulator at the receiver module. The microproc-
essor will then save all data and write an error message to the display.
If the power supply is completely lost, the RM2042 will simply be turned off and when the power supply
is re-established, the RM2042 will be restarted by a power on reset pulse, generated at the microproc-
essor module.
But if the input power supply only drops out shortly, the 5V may not be lost completely, because the
capacitor C3 will hold this voltage for about 20msecs. If the 5V supply for a short instant drops to about
4.5V, the microprocessor will probably lose control and may then by an accident overwrite someimporten
data. To avoid this situation it is necessary to reset the microprocessor, which is done by the power failure
reset circuit at the interface module. This circuit is build-up around the voltage comparator U2.3 and use
a divided part of the 10V supply voltage as reference. The capacitor C63 is used to hold the reference
voltage and the diode D7 avoid discharging backward to the 10V supply, when this drops out. Under
normale operation condition, the voltage at the noninverting terminal will be higher than the reference at
the inverting terminal and the output voltage will then be high. If the 5V supply voltage shortly drops below
4.5V, the voltage at the noninverting terminal will be lower than the reference voltage and the output
voltage will then go low. This will hold the microprocessor in reset in a periode, determined by the capacitor
C27 and the two resistors R27 and R75.
S.P. BUS INTERFACE
The serial S.P. bus interface is implemented in order to be able to control a connected S.P. VHF
transceiver. The connected VHF has to have a similar serial interface in order to be fully controllable for
automatic/semi-automatic operation. If the connected VHF does not have a S.P. bus interface RM2042
can only function as a DSC encoder.
Data is sent and received by the UART U9. The transmission rate is 4800 baud, even parity, 8 data bits,
and 1 stopbit or in RS232 terms 4800, E, 8, 1. When the UART are ready to transmit another databyte,
it uses the TXRDY pin to interrupt the microprocessor.
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RM2042
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