On Mon, 16 Mar 2026, Gary E. Miller wrote:
If the PPS in from the GNSS receiver is connected to the DCD pin on the serial-to-USB chip, then the host sees DCD toggle, and can use DCD as PPS. Accurate to about 1 ms. Better than nothing.
Sometimes it's CTS, which is actually better, since it's part of the standard four-signal interface, while DCD and DTR aren't. AFAIK, GPSD checks both.
The 1ms is based on the driver's polling rate, and not anything inherent in the protocol. But since the intended use is for modem-control signals, the 1ms interval is considered plenty fast enough.
Fred Wright
