Pretty dramatic difference between a "real" serial port and USB. Like two orders of magnitude or more.
If you computer lacks a serial port, just buy a new computer. The Raspberry Pi or the like costs about $40. But the money you save on electric power will pay off that $40 in less than a year. Why is this? the serial port has a pin that is tied to an interrupt. If you read the code associated with that interrupt it is like maybe 4 or 6 lines of C and VERY simple. USB on the other hand is packetized. Nothing happens on till a block of data comes in and then it is quite complex so the time from the pin going active to the internal counter being sampled is quite variable I said "two orders of magnitude" it might even be three orders. On Mon, Feb 13, 2017 at 8:07 AM, Ruslan Nabioullin <rnabioul...@gmail.com> wrote: > Hi, generally speaking, what are the performance differences between the > following: 1. direct RS-232 (i.e., what I believe is a standard PCI card > offering RS-232---essentially UARTs interfaced more-or-less directly to the > PCI bus); 2. RS-232 via USB; 3. PPS decoding PCI cards (which might also > have an IRIG input or even an onboard GNSS receiver). > > Thanks in advance, > Ruslan > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.