In both Baudot and ASCII an idle keyboard produces a constant MARK signal
(loop current 'on' for a TTY machine), thus no signalling changes. In
Baudot/RTTY
it's common practice however to periodically emit what is called a 'diddle'
when
the keyboard is idle. Normally a LTRS character is used as the 'diddle'.
This
helps the receiver stay better synchronized to transmitter. Different
software
can be programmed to emit constant 'diddles' or to emit them about once a
second.

-- Tom



wrote in message
ups.com...
I'm trying to write a program (for my own education) that will transmit
RTTY. I'm having some difficulty determining the exact format. From
what I've observed from MMTTY, an idle keyboard has a 22ms space tone
followed by a mark tone until the next space tone. I would have
assumed that a standard letter/8bit transmit would last 196ms (22*8),
but after recording it with a wav recorder and viewing it, it appears
to be shorter (168ms or so, +/- 10). I'm not sure if the recorder is
not accurate with timekeeping, or if I don't fully understand the
format.

I would like to believe the standard format for a letter/8bit transmit
is a start bit (space), data bits (marks/spaces), and two stop bits
(space), *ALL* of which are 22ms long. Is this statement correct?
Thanks in advance,
Dave