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	2 days ago	18 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
Regression Version
Affected Sets / Systems

Attached Files

No.24624 cuavas Administrator 1 day ago	0 is the active state for RS-232. The issue is elsewhere.
No.24648 Robbbert Moderator 19 hours ago	"The cause was found in source" - how do you know that is the cause? Did you do testing with other values?
No.24649 Marcher Tester 18 hours ago	My apologies, it was my bad. No, I didn't test the emulator with other values. I'm quite new to the forum, so could you please tell me if bugs related to external images (not from software lists) are being considered? This bug is closely related to MacTerminal application. Therefore, if it's acceptable, I'll just edit the report to remove all unverified information.