Regarding Chen's comments about bit-banging and timing irregularities:
When MMTTY is used for FSK in its "native" mode (without EXTFSK), it
relies upon the UART to do the timing, so there should be no timing
problems there.
When EXTFSK is used, it does indeed bit-bang on either TxD, DTR or RTS
(or even on lines from a parallel port). However, according to the
documentation for JE3HHT's implementation of EXTFSK (comfsk105.zip), it
uses the multimedia timer to control timing. Is this multimedia timer
the same as (or similar to) the isochronous mode timer used in the audio
device class? If it is, then the timing of FSK produced by bit-banging
with EXTFSK should be just as accurate as the timing of an on-off keyed
tone, or of AFSK produced directly by the sound card. And of course if
this is the case, there would be no advantage to generating an on-off
keyed tone from MMTTY compared to using EXTFSK.
73,
Rich VE3KI
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