3 ms·

You typically use a dedicated GPIO pin to read the PPS signal as the authoritative start-of-second.

• tyingq 5y ago
  Ah. They appear to be using the RS232 DCD line for that.
  • h2odragon 5y ago
    RI can trigger interrupts
    • mbbrutman 5y ago
      This particular machine was the victim of some cost cutting, so there is no RI line. Data Carrier Detect is available and it is usually used for this. (I got my wiring inspiration from other projects.)
• toast0 5y ago
  If you can, a PPS signal is ideal; sometimes they're not available though (I've got a setup with an LTE modem that includes a GPS signal, but no PPS. Without a PPS signal, and through the many layers, it's kind of meh accuracy, and I wouldn't export its time to anyone, but it's better than nothing when I don't have any external communications.