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Question: Does the program work with virtual COM ports? USB-COM converters?

Answer: Absolutely!


Question: Why COM port doesn't open?

Answer: Probably, another program already uses it (the selected COM port). It can be a service application, for example.


Question: What to do?

Answer: Close the application that uses this communicative port (for a DOS application close also a DOS session window). Alternatively, use another communicative port. Probably, a COM port wasn't properly closed.


Question: Is it possible to set variable data transmit rate or transmit 9 data bits?

Answer: No, the Windows operating system doesn't have such the feature.


Question: What socket type to use: DB25 or DB9?

Answer: It does not matter. All modern computers have DB9 only. Alternatively, they do not have DB9 sockets at all.


Question: What cable do I need: straight or crossed (null-modem)?

Answer: It depends on your device. Generally, you should use a null-modem (crossed) cable with the following layout:


Device   |   Computer


RXD <--> TXD

TXD <--> RXD

GND <--> GND


If a device uses special signals like DTR or RTS, and you don't want to use hardware data transmit control, you need to connect pins 7 and 8 of the DB9 socket on the device side.


You can find more hardware related articles on our site https://www.aggsoft.com.