+ AA6YQ comments below
Greetings! I'm stuck right where KR9U landed, have reviewed many useful videos, docs & posts, but I'm still stuck! Tone, not FSK, being transmitted using WW/RTTY-FSK.+ The IC-7300 driver creates a single virtual serial port for transceiver control whose RTS or DTR signal can be configured to convey the FSK signal via the radio's USB Keying (RTTY) menu; if this port is being used for transceiver control, however, its RTS or DTR signal cannot be used as the FSK connection.
+ (Note 2.d in <https://www.dxlabsuite.com/dxlabwiki/FSKConnection>)
+ Thus if you want both transceiver control and transmission via RTTY FSK with an IC-7300, you'll need an external interface to generate the FSK signal from the RTS or DTR signal of a serial port not being used for transceiver control. Device drivers for Icom transceivers like the IC-7610 and IC-7851 create two virtual serial ports, enabling one to be used for transceiver control and the other to convey the FSK signal without the need for an external interface.
+ When transmitting via RTTY FSK using the MMTTY engine, EXTFSK64 specifies the serial port and signal used to convey the FSK signal. See step 7 in the "Configuring WinWarbler for FSK operation.