As Tom, WB6B suggests, an important reason for displaying the TX frequency in CW modes is that you need to know that when you
hit that key that you are transmitting in-band. It is more important to know your TX frequency than your RX frequency and this is also
the convention used on most commercial HF rigs.
I only had the original uBITX code installed for a day but I do seem to recall that there was no explicit CW mode.
The CEC code does have explicit CWU and CWL and as I stated, once you have a station properly tuned you should be able to toggle
back and forth between the two CW modes and still have the received station in the filter passband. There may be a slight shift in received tone
(nothing is perfect) but it should be very close.
I also believe that what Tim AB0WR suggests regarding changing the BFO frequency is correct.
If you haven't moved the VFO the frequency it's frequency shouldn't change except to apply a +/- offset equal to the sidetone frequency on RX (the TX carrier frequency stays the same and should be the dial frequency as stated above). Switching back and forth from CWU to CWL should change the BFO frequency (which only affects RX) to allow the switching of the selected sideband. The change in BFO frequency plus the application of the RX offset with the correct sign to the VFO determines the change in RX frequency on the CW mode change.
If you must display the actual RX frequency as the dial frequency then it has to change when you change from CWU to CWL. Changing the TX frequency
as it currently does is incorrect. Also I would suggest that if the dial frequency remains the RX frequency, then the display should change on TX to show the
TX frequency (i.e. carrier frequency) and then back again on RX.
As Allard, PE1NWL stated in an earlier posting on this same topic ... we went through pretty much the same discussion on the operation of the BITX40
and came to the conclusion that the display frequency on both CWU and CWL should be the TX (carrier frequency) and that is what Allard implemented in
his Bitx40 code.