[GreenKeys] ASCII <-> Baudot algorithm

[Jim Haynes]

The early writers on ham RTTY advocated disabling unshift-on-space.  I
guess the reason was that not all machines could do it, so you didn't
want to let it do the unshifting for you, when it might leave the other
guy's machine in FIGS.  My feeling was like yours, that you'd like to
have USOS so the machine would come out of FIGS case if it got there
accidentally; and you could accomodate the other machines that don't
do USOS by being careful how you send.  That is, always send a LTRS
when you have beein in FIGS and want to type letters.  And always send
a FIGS following a space if you want to remain in FIGS case.

As you note, machines in weather service were arranged with USOS disabled
because most of the material is figures and it saved time to not have
to insert a FIGS character after every space.  Whereas in more ordinary
communication service strings of figures with spaces interspersed are
fairly rare, so it saves time to have the machines unshift on space and
not have to send the LTRS character.

So in the software that's simply another option you have to consider.
You have a variable that holds whether the simulated machine is in
LTRS or FIGS case, and that controls which of two translation tables
you use.  The variable always goes to LTRS when a LTRS is received
and always goes to FIGS when a FIGS is received.  The option is whether
it is also set to LTRS when a space is received.