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Audible indicators
Audio files including alarm tone, button tone and pulse tone are burned in a serial flash
memory in advance. To give out a sound, the CPU reads audio data from the flash
memory and controls the puse-width modulation (PWM) to give out a audible signal.
The pulse oximeter supports pitch tone and multi-level volume. The speaker is
connected with the main board and the audible signal is provided by the main board.
2.3.1.4 Communication Interfaces
RS232 port
The RS232 port implements communication through the CPU’s UART module and the
RS232 drive chip. The RS232 drive chip which is integrated in the PC communication
cable is electrostatically protected. The CPU’s UART module has an external drive IC
to enforce driving and ensure protection.
Infrared port
The BF 531’s UART supports infrared transmission. The transmitted and received
signals are connected directly to the infrared IC.
2.3.2 Power Supply
The power module provides hardware for power supply management. It detects the level
required by all hardware, the priority of power supply type as well as the power supply status.
It is also controls the power indicating lamp and real-time clock, manages battery charging
and communicates with the main control unit.
The block diagram of the power module is shown below:
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