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SP200/210 Maxon SP200/210 Radio
Issue 1.0 DETAILED FUNCTIONAL DESCRIPTION
03/01 Page 5-1
5 DETAILED FUNCTIONAL DESCRIPTION
5.1 Introduction
This section provides a detailed description of the operation of the radio.
5.2 Common Circuits
Power Circuits
Battery voltage, or external voltage through the accessories connector, is applied via a 4A fuse (plus
diode protection) directly to the RF power module and, after the on/off switch, to the dc to dc converter
and voltage regulator. The majority of the circuitry is powered via IC1, which regulates the +7.5V dc
supply down to +5V.
Transistors Q2 and Q32, in conjunction with the Tx Enable and Rx Enable lines from the
microcontroller, apply +5V Tx or +5V Rx to the relevant circuitry during receive or transmit. Thus, for
instance, the receive front end amplifier is only powered during receive and the power control IC is
only powered during transmit.
It is possible to program the radio for power saving. This mode causes the microcontroller to pulse the
Rx Enable line high and low for periods between 100 and 300mS. The time may be selected when
programming the radio. As soon as the radio detects a signal it switches into normal mode.
Microcontroller
The microcontroller (IC403) is a One Time Programmed Processor chip based on the Hitachi HD3837
processor with onboard ROM and RAM.
It controls all functions performed by the radio, in conjunction with control signals from push buttons,
switches etc. It controls the data to/from the EEPROM and to the PLL IC, Audio ASIC as well as
controlling external data from the programmer and alignment interface. The microcontroller generates
the enable lines, controlling routing of signals and the indicators (LED,LCD and bleeps).
The microcontroller also generates and decodes the SAT tones (filtered by the ASIC).
EEPROM
Relevant channel information, such as Rx / Tx frequencies and CTCSS / DCS codes, is stored in the
EEPROM (IC404) which is a X25330. This information may be programmed and erased via the
accessories socket. Certain parameters can also be altered via the pushbuttons and keys on the
radio, i.e. scan channels and priority channel. The EEPROM has 32768 (8x4096) capacity and data is
written serially.
Channel Select Circuit
Up to 199 channels may be selected, using the channel keys on the front panel. Pressing the channel
keys earths pins 40 and 41 of the microcontroller, so enabling the decoding for the appropriate Rx and
Tx frequencies, and associated data, to be selected from the EEPROM.