User Manual

SECTION 1: THEORY OF OPERATION
~\Technical Documentation\System Manuals\FCC-Reports\DT450-FCCRpt.doc Page 5
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DT450 Mobile Data Radio Board Circuitry
The DT450 Mobile Data Radio works within a frequency range of 400 to 512 MHz.
The following section provides detail views and key areas on the DT450 Mobile Data Radio circuit board
especially useful during troubleshooting.
Microcontroller
The microcontroller (U43) is a major component of the radio as it manages the operation of the radio
loading the selected transmit/receive frequencies into the injection sythesizer. It also controls the
operation of the modem, and determines which receiver provides a better signal from a given
transmission. It provides transmit time-out protection in the event a fault causes the radio to halt in the
transmit mode. It utilizes a Reduced Instruction Set Computer (RISC) architecture which provides low
power operation and a powerful instruction set. Other features include a watchdog timer, serial UART,
two 8-bit timers, and 2 kB of electrically erasable programmable read only memory (EEPROM) storage.
The EEPROM RAM stores the setup data entered by the technician even if there is a loss of power.
Support circuitry
The support circuitry consists of the following:
 A Supervisor Control Chip (U4) providing power-on reset.
 The clock controls microcontroller operation and is generated by crystal Y4 and a Pierce oscillator
circuit (inside the U43-microcontroller).
 The latch (U40) decodes low order address bits (A0-A7) from the address/data bits (AD0-AD7). It
enables Address Latch Enable (ALE) output of U43 and the bits are used by the modem and
synthesizer circuitry.
 A 32Kx8 Static RAM Chip (U41) provides temporary storage of the radio’s configuration data
facilitating the technician with access to make changes.
 Glue logic is also an important part in the microcontroller section. The RAM chip select (CS) and
modem chip select (MODEMCS*) command lines are created by U46. These gates decode four (4)
high order address bits (A11-A15), plus the read (RD*) and write (WR*) command lines.
Input/Output
Input/output components convert serial and handshake data from the modem section to RS232 levels,
and vice-versa. Chip U47 is an RS232 transmitter and receiver. It converts data in 5-volt logic form to
data in +/-12-volt form, as required by the RS232 standard. A charge pump power supply on the chip
converts the +5-volt DC logic power on pin 16 to the +12-volt and –12-volt levels required utilizing
capacitors C199-C202 to generate these voltages.