Raymarine Limited. Registered in England. Company no. 1177969
Page 17
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no matter what the setting of the volume control pin, by matching the volume control setting with an
increase or decrease of key-beep signal level.
On-Hook/Off-Hook sensor.
A uni-polar hall effect device provides a method where the system can detect if the handset is placed
in its cradle or not. It provides a logic level output suitable for feeding into a port pin of the
microprocessor when either pole of a magnet produces a magnetic level of at least 55 gauss within its
vicinity. A ferrite magnet placed within the body of the cradle is used to activate the sensor when the
handset is attached to the cradle.
Distress Button
The distress button is used to send DSC distress messages. It is monitored directly by a separate
processor pin so that’s its operation cannot be masked by any other key press.
PTT (Push to Talk)
The PTT line from the main processor is used to set the transmitter into transmit mode whenever the
PT button is pressed by pulling the PTT line low. However, the PTT line is also used to set up initial
communications between the radio processor board and handset at power on, and a data stream is sent
down this line at this time. The data stream is interpreted by the micro-controller during initialization.
The PTT switch is monitored by the processor and is therefore ignored if pressed whilst initial setup
is undergone. After initialization has completed, the PTT switch position is echoed onto the PTT line
by TR10, operated by the micro-controller.
