The following is the connection method of ttl to 232:
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Connect pin 2 and pin 3 of the serial port to a level conversion chip (such as SP3223, SP3423, etc.), and then connect to a 5V power supply. If you need to transmit a longer distance, you can use a 9-pin serial connector and place the level conversion chip at the signal sending end, and use the same level conversion chip and 9-pin serial connector at the receiving end.
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It should be noted that when ttl to 232, the appropriate level conversion chip and serial port connector need to be selected according to the specific situation, and ensure the stability of the power supply voltage.
The ttl register is set to shift mode (shift left) with instructions, the lowest output is connected to the input end of serial port 232, and each shift outputs a bit to the 232 interface