[GreenKeys] Model 15 + C-64 Baud rate question

[Jim Haynes]

Putting a delay between characters will not help, because the individual
bits are still shorter than the machine expects.

The selector cams sample the state of the selector armature in a narrow
slice of time.  You want these samples to take place in the middle of
the signal pulses, so that if the boundaries between pulses are off
for any reason the selector has the best chance to get a correct
selection.  All this timing is derived from the START pulse when the
selector magnet goes spacing and allows the selector cam clutch to
start rotating.  The range finder moves the relationship between
the sampling pulses from the cams and the beginning of the START pulse.

The process of adjusting the range finder between its limits while
receiving a signal is intended to set the sampling time as near the
middle of the bits as possible.  The errors you get at the extremes
are caused by the sampling time being so early or so late that the
selector armature is moving at the time of sampling.

If the motor is running slow (relative to the incoming signal) the
transitions between bits will steadily get ahead of the optimum time
for selection.  You may be able to get by with this by advancing the
sampling times to be early.  If you are lucky you don't get it so
far advanced that it samples at the beginning of the #1 pulse, nor so
retarded that it samples at the end of the #5 pulse.

If you don't have to use the C-64, if you can just use an old PC, the
old serial ports can be set to run at 45.45 baud.  But if you must use
the C-64 then it would seem like getting the amateur radio program for
it would be the easiest way to go.