Table of Contents
Advertisement
2.2.2 Receiver Board (AMP 01P5725)
On this board the FM and FS signals received through the receiving transducer is
frequency-converted to be applied to the succeeding DISP board.
The received signals are sent to the first mixer where the frequency of the signals are
converted to 455kHz IF frequency. The output of the first mixer is amplified and applied to
the second mixer and IF amplifier. The output signal is 9.5+0.5 kHz (2nd IF frequency).
Amplifier gain and selection of the first local oscillators are controlled by the DISP board.
2.2.3 Display and Signal Processor Board (DISP 01P5726)
The DISP board incorporates two microcomputers, SUB and MAIN for enhanced
processing speed. The SUB computer is a single chip MCU (Micro Computer Unit) which
has a built-in ROM and RAM. Its major function is detecting the SYNC codes from the echo
signal and sending them to the MAIN CPU. The MAIN CPU incorporates a built-in 256 byte
RAM but no ROM. It uses an external ROM. The main functions are arithmetic processing
of the temperature and depth data, the reading of operator's commands from the panel
keys and writing the processed data into the video RAM via the gate array. It also acquires
ship's speed data by communicating with external navigational equipment in the Furuno
CIF format and generates the clock signal for the SUB MCU (SYNC code detector). The
video RAM has three picture pages and one scale/character page. This enables instant
switchover to the picture page selected by the presentation mode.
•
Echo Data Acquisition
The FM echo signal (9.0 - 10.0 kHz) from the AMP board 01P5725 is led to the
CPU-controlled low-pass filter U19 via selector U11. The selector selects the external
(playback) signal if the picture recorder MT-12 is connected. Then, it is applied to the
succeeding AM and FM detector circuits after being amplified by the buffer amplifier.
The AM detector functions to detect received signal strength. The FM detector
demodulates the received FM signal.
Signal acquisition is performed by the combination work of the MAIN and SUB CPUs. First
the SUB CPU detects the Down SYNC code from the received signal then the acquisition
starts. The acquired data is directly transferred to the MAIN CPU's RAM (DMA transfer;
Direct Memory Access) and interference rejection is executed if the "Noise Limiter" is
turned on through the menu. Then the data is transferred to the video display RAM
according to the presentation mode and the control of the gate array. See the signal
acquisition sequence on the next page.
2-12
Advertisement
Table of Contents
