YMODEM protocol problem with Virtual COM

[Mikle]

I encountered a strange problem that occurs when implementing a virtual com port.
Virtual port is functioning normally, but when I send a file from hyper terminal using YMODEM protocol, then nothing happens.
There is not any interrupt USB. HyperTerminal after the timeout sends a code of 0x18 (CAN).
And as with all other terminals. No change in what the options do not affect the result.
I used the example of the STM.

[Jan Axelson]

If you can't send anything from hyperterminal, check all of the port settings in hyperterminal. 

Jan

[Mikle]

I get the characters from the hyperterminal in my USB virtual COM application, but did not get any character when I send a file by YMODEM protocol.
А feeling that the transfer does not start at all.
Is it possible that the YMODEM try to reads the signals of modem that are not exist physically?

[Jan Axelson]

Ymodem requires responses from the receiver:

http://www.techfest.com/hardware/modem/xymodem.htm

Jan

[Mikle]

The problem is that if I send a file from hyperterminal  using Ymodem protocol, at a reception I do not get a single character.
Тhere is no start file transfer. If the file is sent as text from hyperterminal to my embedded Apps is no problem.

[Jan Axelson]

I'm not an expert on ymodem, but take a look at the reference I suggested above, in particular:

6.3.2  Receive_Program_Considerations
The receiver has a 10-second timeout.  It sends   a <nak>   every time it
times out.  The   receiver's first timeout, which   sends a   <nak>, signals the
transmitter to start.  Optionally, the receiver   could send a <nak>
immediately, in   case the sender   was ready.

Jan

[Mikle]

Hi Jan,
I read a bad description of the protocol.
Тhe receiver really needs to send at the beginning of the character "C" to the transmitter in case 1k ymodem
If it does not make the transmitter does not begin the session.
Thank you