Selection
Cabinet timing: how NTP, Modbus, and 1PPS split
IPCs use NTP, PLCs use Modbus millisecond calendars, scopes see 1PPS—never one shared figure.
Updated 2026-08-22
Decision
Wire and accept per channel. The 1231 has no IRIG.
Notes
SY-1231 can serve Ethernet NTP, RS-485 Modbus absolute time (including ms), TTL 1PPS, and minute PULSE together. Include in supply and acceptance only the terminals that will be wired.
IPCs and logs use NTP (UDP 123). PLC/SCADA polling uses Modbus at 1 ms resolution—not nanosecond timing.
For a hardware second edge, use the 1PPS jack (3.3 V). PULSE on 4-pin Pin4 is a minute pulse—not 1PPS and not IRIG.
Power is single-path: one AC or DC inlet at a time. Confirm LOCK before accuracy-related acceptance.
Need IRIG-B or stamped NTP? See coming SY-4096. Multi-port / dual supply → 8640 roadmap.
FAQ
- What is the decision?
- Wire and accept per channel. The 1231 has no IRIG.
- What are the key points?
- IPCs use NTP, PLCs use Modbus millisecond calendars, scopes see 1PPS—never one shared figure.