Why doesn't the CY4601 USB to Serial reference design work will all RS-232 devices?

Question: Why doesn't the CY4601 USB to Serial reference design work will all RS-232 devices?

 

Answer:

The USB to Serial reference design isn't guaranteed to work with all RS-232 devices.  Many RS-232 devices were developed to use the 9 signals in their own proprietary ways.  Some RS-232 devices can also have certain timing requirements in their startup or initialization sequence.

This USB to Serial design was developed under the assumption that the 9 signal lines will be used as defined by the TIA/EIA-232 standard.  Any special requirements of the 9 signal lines will require USB to Serial firmware modifications.