Difference signal betwenn RS232 to UART and USB to UART

Hi everyone,
I am facing with a problem about changing DB9 port to USB port to adapt to new computer generation.
I download an application that has a Graphic user interface was written on Windows XP, use DB9 port connect to a board has a MAX232 IC to convert signal from RS232 to UART to communication with MCU with diagram:
PC -- DB9 cable -- RS232 to UART -- MCU.
My computer running windows 8, which does not have DB9 port, so I bought a board that convert USB to TTL (uart). So now my diagram is:
PC --- USB cable -- USB to TTL board --- MCU.
With my connection (using USB to TTL), I can not use the GUI to read or write signal because the GUI waiting for a "\r" ascii 13 or CR to parse data. I can confirm that because I can use a serial port software such as putty to type the command and communication with the board.
So my question is when I change RS232 to USB, will my signal be changed? if yes, could you suggest for me a solution?
Thank you so much!

Hi,

usually it should be possible.

What about comm port settings? baud rate handshake...
Some USB to TTL converter invert the signals. this can be overwritten.

What about the signal levels on "TTL" side? Are they true TTL or CMOS, LVCMOS, LVTTL? What voltage level?

Do you have a scope to watch the signals?

Klaus

Dear KlausST,
Yes, it is TTL, I can view help text and descriptions from MCU via terminal screen, but I can not receive it on the GUI, so I have set a right baudrate also wiring. It just lack of some characters such as \r or \n.

There's an outfit that makes many USB-XX chips, I'm
having trouble recalling the name - FTDI maybe? There
may be an existing (if obscure) solution for adding USB,
maybe without having to ditch the RS-232 (which may
still have a lot of life left in it for factory automation).
The chip set maker was good about providing drivers
back when I was looking at stuff using them (like
GPIB<->USB converters dongles).