DANIELS
ELECTRONICS LTD.
TM
VHF Enhanced Extra Wideband Receiver Instruction Manual IM10-VR3H040-AB
3-13
3.3.4
Synthesizer Digital Circuitry (Digital Board)
Microcontroller U4 generates control signals utilized within the synthesizer module. U4
communicates with synthesizer IC U10, monitors the synthesizer lock detect, manages PTT
input and output and determines the operating frequency by reading channel number information
from either the four rotary Binary Coded Decimal (BCD) switches mounted on the main
Transmitter and Receiver PCB, or by reading four externally driven CHANNEL SELECT lines.
Microcontroller U4 is also designed to communicate with Daniels SYNTHESIZER CHANNEL
PROGRAMMER (CP-SC-3) through I/O lines TX DATA (P1-17), RX DATA (P1-9) and
BOOTSTRAP (P2-2). This external programmer places the operating program in non-volatile
microprocessor memory and programs up to 15 user defined channel selections. An internal
"watchdog" timer provides robust software protection in all operating modes.
Data communication between the digital and analog circuit boards is achieved through four
optical transmitters (U5 through U8) and one optical receiver (U9). The optical interface
provides a fully isolated inter-board data communications link designed to prevent digital noise
from interfering with sensitive PLL circuitry.
3.4
Frequency Control
3.4.1
BCD Switch Frequency Control
Selection of the desired synthesizer output frequency is straightforward. If all four of the
CHANNEL SELECT lines (CHAN SEL3 - CHAN SEL0) are pulled low (to GND), the
synthesizer will scan the four BCD switches (FSW1 - FSW4) located on the receiver and
transmitter main circuit boards via connections SW1 COM - SW4 COM and PC4 - PC7 and
establish the operating frequency from these switches. The four CHANNEL SELECT lines,
CHAN SEL3 - CHAN SEL0, are connected via the MT-3 transmitter or receiver main board
module connector to the M3 motherboard subrack. These lines are by default normally pulled
low (to GND) via jumpers located on the M3 motherboard subrack.
If any one of the CHANNEL SELECT lines are pulled high (to +9.5 Vdc), then the synthesizer’s
frequency of operation will be determined by the CHANNEL SELECT lines and not the BCD
switches. Up to 15 separate channel frequencies can be pre-programmed into a ‘table’ in non-
volatile microprocessor memory and accessed through binary interpretation of the CHANNEL
SELECT lines. The most significant bit (MSB) in the CHANNEL SELECT binary code is
represented by CHAN SEL3 and the least significant bit (LSB) is represented by CHAN SEL0.
For example, if all CHANNEL SELECT lines are pulled high, (i.e. binary ‘1111’) then the 15
th
frequency entry in the internal channel table will be selected. The channel table is normally pre-
programmed at the factory to user specifications, but may be programmed in the field using
Daniels SYNTHESIZER CHANNEL PROGRAMMER (CP-SC-3).
