Chip: Domestic MAX3232CSE 

Voltage Range: 3V ~ 5V 

Highest baud rate: not recommended higher than 120kbps 

Size: 9.4mm * 15.9mm 

The following is a block diagram positive and negative, power supplies are connected together on both sides, and then only to the side, the two sides of each of the separate channels can be used, arrows indicate the flow of signals, instructions are input to the inside outward Description is the output, RS232 character near the end of the RS232 level, near the end of the character TTL TTL level