Adcon A440, Technical Reference Manual

Page: 11 / 47

11
The Microcontroller and the Power Conditioning Sections
• Implements a serial Command Line Interface (CLI)
The chip operates at its maximum speed, in this case 4 MHz (the “L” version), and
uses a crystal (X2) for the on-board clock generator. The real time clock is imple-
mented by means of a 32.768 kHz crystal (X1) connected on the internal Timer/
Counter0.
The radio unit is controlled via the SPI bus (to set the PLL chip parameters) and via
several ports of the microcontroller for such operations as transmit and receive. In
addition, the high current 5 volt LDO voltage source (U4) is switched on before the
radio module’s PA is activated. The power output is adjusted by means of an elec-
tronic potentiometer (U2).
The A/D subsystem is used to sample the RSSI and Pout inputs. A stable 2.5 Volt
reference supplied by U3 is applied to the A
ref
pin. The reference is powered by the
microcontroller only when sampling the A/D input.
The serial interface is implemented by means of the built-in UART. Both the RS-232
and RS-485 interfaces are implemented using Maxim chips (U12 and U17 respective-
ly). The serial interface mode is selected by means of a pair of jumpers (J1).
An additional amount of 32Kbytes RAM is provided to the main microcontroller; the
RAM chip (U8) is attached to the multiplexed bus of the microcontroller with the aid
of a latch (U10).
A brown-out supervisor chip (U14) is used to assure a smooth start-up of the micro-
controller and avoid possible erratic behavior when the supply level descends below
the minimum operating value (2.7 volts).
A LDO voltage regulator (U16) is used to provide 3.3 Volt power to the main com-
ponents on the board.