Ray 240 Handset Circuit Description - Raymarine RAY 240 Manual

RAY 240 Handset Circuit Description

Power Supply
Power is supplied to the handset from the main radio via an extension lead and waterproof connector.
There is no provision for reverse supply protection, as this is impossible if the connectors are fitted
correctly. Provision for reverse polarity protection is provided inside the main radio. As such, the
polarity of the voltage to the handsets should always be correct.
The power supply can range from 9V to 25V, accounting for the wide range of voltages that can be
obtained from a discharged, or fully charged nominal 12V lead-acid battery, up to inadvertently
connecting the unit to a 24V system.
An on-board 3.3V regulator reduces the voltage to that necessary for the microprocessor, display and
ancillary equipment to run. Because of the low current requirements placed on the 3.3V supply, an
external heat sink for the supply regulator can be dispensed with, even allowing for the high volt drop
across the regulator. The raw 12V (nominal) voltage is also used to drive the LED backlighting where
relatively high currents are required, where this reduces the load on the 3.3V regulator, and for the
Seatalk interface where 12V is required to attain the signal level required. If the system is connected
to a 24V supply, the LCD backlighting is disabled as excessive heat dissipation in the transistor
drivers (TR15,TR16,TR17)will result if the LED's are lit.
Micro-controller
The micro-controller is a Texas Instruments MSP430F135. This is a very low-power 16-bit micro-
controller with 16kBytes of Flash memory and 512 Bytes of RAM. The on-board 12bit ADC
converter is unused in this application. The micro-controller reads the keyboard, drives the LCD
display, and the backlighting. In addition, it communicates to the main processor in the radio box via
a Seatalk interface, operates the PTT and audio volume controls, and provides provision for a 'key-
click' audio indication. It operates from a 3.3 supply derived from the main battery supply of 12V
nominal by the LM317 regulator.
Display.
The display is a 128 pixel by 64 pixel full graphic monochrome FSTN LCD display module. The
module is a Chip On Glass (cog) construction with interconnections to the processor via a 30 way flat
ribbon connection. The controller chip is attached directly to the glass substrate of the display and
runs from a 3.3V supply. This greatly reduces the number of interconnections required between the
display and processor. The display requires 4 control lines in addition to the 8 data lines to send
information onto the screen. The rest of the connections are used for the capacitors required by the
on-chip voltage generator circuitry of the controller chip.
Keyboard.
The handset contains a total of 27 pushbuttons, of which only 25 are in the key-matrix. The
remaining two keys are DISTRESS and PTT. These keys are read separately by the processor on
dedicated input ports. The key matrix can thus be driven to allow only one key to be active at any
time and will not 'lockout' the distress key or PTT key if any other key on the keypad is pressed.
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