Twinleaf RS422 (3.3V Differential Serial)
The Twinleaf differential serial interface conforms to the RS422 standard with additional specifications for power supply and synchronization. Users can choose a single USB-RS422 adapter (provided with any RS422 device) or an 8 channel hub, HUB-8RS422, which provides time synchronization and GPS.
Physical interface
An 8p8c (RJ-45) connector is provided for connections using standard CATx ethernet-style cable.
| Pin | Signal | Wire color |
|---|---|---|
| 1 | TX+ | Orange/White |
| 2 | TX- | Orange |
| 3 | RX+ | Green/White |
| 4 | +15-48V | Blue |
| 5 | Ground | Blue/White |
| 6 | RX- | Green |
| 7 | PPS+ | Brown/White |
| 8 | PPS- | Brown |
Digital signal nominally employ ±3.3V differential signaling. Twinleaf uses LTC2865 transceivers to drive all three TX, RX, and PPS signal lines, providing high ±25V common mode tolerance and ±15 kV ESD protection. The lines are terminated at the receiver with 120 Ω.
Power may be supplied up to an absolute maximum of 60 V to overcome resistance in long cables.
The PPS signals are not required for operation, but are used to discipline and synchronize an oscillator at the sensor. The sensor synchronizes to a rising edge and disregards falling edges.
Applications
The RS422 interface supports long cable lengths, up to 1 km with appropriate considerations for system power and cable resistance. Pictured above is a 100 m spool of neutrally buoyant cable attached to a VMR sensor. The cable passes through a slip ring and connects to a HUB-8RS422 host unit.