SerialX.begin - support 7 bit modes. #391
                
     Open
            
            
          
  Add this suggestion to a batch that can be applied as a single commit.
  This suggestion is invalid because no changes were made to the code.
  Suggestions cannot be applied while the pull request is closed.
  Suggestions cannot be applied while viewing a subset of changes.
  Only one suggestion per line can be applied in a batch.
  Add this suggestion to a batch that can be applied as a single commit.
  Applying suggestions on deleted lines is not supported.
  You must change the existing code in this line in order to create a valid suggestion.
  Outdated suggestions cannot be applied.
  This suggestion has been applied or marked resolved.
  Suggestions cannot be applied from pending reviews.
  Suggestions cannot be applied on multi-line comments.
  Suggestions cannot be applied while the pull request is queued to merge.
  Suggestion cannot be applied right now. Please check back later.
  
    
  
    
As per the forum thread:
https://forum.arduino.cc/t/uno-r4-and-serial1-different-nr-databits/1192974/9
Sketches that tried to use the standard modes such as Serial_7E1 Would not work and sounds like they would hang.
This sketch simply duplicated the 8 bit modes, in the switch statement, and changed _8 to _7... So for example:
There was already support for handling this in the FSP layer. I verified that 7E1 and 7O1 worked using logic analyzer. Also verified that the standard 8N1 still worked.
Note: The ArduinoCore-API file HardwareSerial.h has many other defined modes, which are probably
not supported, on the UNO R4, such as: SERIAL_5E2
Which the switch statement still does not handle, and the uart_cfg items will not be set... But that is beyond this fix.