09534: DCD/DSR/CTS permanently hardcoded to 0 in null_modem.cpp

ID	Category [?]	Severity [?]	Reproducibility	Date Submitted	Last Update
09534	Media Support	Trivial	Always	22 hours ago	7 hours ago

Tester	Marcher	View Status	Public	Platform	MAME (Official Binary)
Assigned To		Resolution	Open	OS	Windows (x64)
Status [?]	Direction Needed			Driver
Version	0.288	Fixed in Version		Build	x64
		Fixed in Git Commit		Github Pull Request #

Summary	09534: DCD/DSR/CTS permanently hardcoded to 0 in null_modem.cpp
Description	Running mac128k and attempting to dial through MacTerminal's Dial dialog (Connection Type = Modem, with tcpser acting as a real modem emulator) consistently reports "no modem found", even when the rest of the path is confirmed working (manually typed "AT"/"ATDT777" gets through cleanly and tcpser replies "OK"/dials out correctly). The cause was found in source, src/devices/bus/rs232/null_modem.cpp, function update_serial(): // TODO: make this configurable output_dcd(0); output_dsr(0); output_cts(0); This is the only place in the entire file where DCD/DSR/CTS are set — they are unconditionally forced to 0 on every device reset and on every speed/parity/data-bits change, regardless of anything arriving over bitb (bitbanger). The only other BITBANGER-capable device in the same directory, rs232_sync_io.cpp, was also checked and shows the same pattern (output_dcd(0); output_dsr(0); hardcoded). In other words, MAME 0.288 has no rs232 device at all that combines socket connectivity (bitbanger) with real DSR/CTS signaling. The guest OS (here, MacTerminal's modem-detection routine) apparently checks exactly these lines before allowing a dial attempt — and since they can never go high, any software relying on hardware modem-presence detection via DSR/CTS is guaranteed to see "no modem", regardless of tcpser settings, bitbanger, or any intermediate tooling.
Steps To Reproduce
Additional Information
Github Commit

Flags	Noted in Source
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Attached Files

No.24624 cuavas Administrator 7 hours ago	0 is the active state for RS-232. The issue is elsewhere.