"David J Taylor" <[email protected]> writes:
>"David Lord" <> wrote in message >news:[email protected]... >[] >> I never scoped mine but it did give a very poor ntp output by one >> of usb-serial I tried (nowhere near that without pps using serial >> port on server and much worse than you reported for yours using >> usb and Windows) and I had no output at all with other usb-serial >> I tried (that works ok connected to a modem) but was ok when >> connected back to serial port of server. I've just checked stats >> on server via serial port for reach !=377 and from 700+ it's < 20, >> which includes lack of sat's in view and INIT. My stats are at >> 30min so for radioclocks only catches about 25% when polled at 64s. >> >> David >Well, it /could/ be the levels causing failure with a USB converter, but >it would surprise me. Much newer RS-232 kit responds, as you will know, >to TTL levels and may not have quite as much hysteresis built in as older >models did. When using a USB converter, I saw a jitter of around 45 >microseconds, compared to a jitter with a direct GPS/PPS connection of 3 >microseconds, but a jitter with a LAN connection of 110-140 microseconds. >I would suspect that figures much worse than that suggest the PPS signal >was not getting through on the DCD line. You need a software breakout >box, don't you, to see how the USB converter actually presents such lines >to the PC! USB only has one data line. It cannot "do" a DCD line except as another bit of serial data, interleaved with all the other serial data. Ie, you are not going to get any good signals for an "interrupt". You definitely need either a real serial port with a true hardware line, or a parallel port to get true interrupts. >Cheers, >David _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
