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RS232 Converter
Designed by Mark Little
Microprocessors such as the AT89C55 have a serial port, but the inputs and outputs are TTL, rather RS-2332 levels.

The RS-232 Converter board provides the conversion between TTL and RS-232 levels. This allows designs using single chip microprocessors to ignore the conversion process as it can be handled independently.

The RS-232 board is mounted by the captive nuts that are used to lock the connector the socket. Best practice is that the wires to and from the 4-pin connector should be support to prevent them putting strain on the Printed Circuit Board (PCB).
The 4-pin connector has the follwing pin-out:
Pin Function
VCC Supply Voltage (+5V) to the Senor.
GND Ground or Earth connection for the supply voltage and the sensor output
TXD TTL Level data to be transmitted as RS-232 port.
RXD TTL Level data received from the RS-232 port.
This converter is only suitable for serial port communications that do not require hand-shaking signal lines such as DTR, DTS, etc. AT89C55 projects that require an RS-232 interface will use this type of interface.