There are two types of USB-to-serial port
One is USB to TTL also known as serial port
The other is USB to 232
The difference between the two is that the RS232 signal has a logic 1(high level) voltage of -15v and logic 0(low level) voltage of 15v
The TTL voltage is 0v-5v, so the two interfaces are not compatible with each other, and a conversion chip such as max232 is required for level conversion
Generally, single-chip computers use TTL serial ports
The industrial computer and other 9-pin serial port are RS232 signals
The easiest way to distinguish is if it is a USB to 9-pin serial port is an RS232 signal
rs232 standard signal serial communication interface. Two rs232 port data to serial communication, must signal. No signal, serial data recognition, communication.