Power over Coax (PoC) for Interface Adapter Modules

Power Over Coax (PoC) is a feature of GMSL and FPD-Link serial link standards. PoC allows DC power to be delivered over the same coaxial cable used for high-speed serial data. An inductive (bias-tee) filter on each end of the cable separates the DC power component from the high-frequency serial signal, allowing both to coexist on the same conductor.

Interface adapter modules can support PoC in one of two roles.
  • Source - the interface adapter module supplies DC voltage onto the cable. This role is the typical configuration for receive-side (deserializer) interface adapter modules that need to power a remote serializer or remote camera.
  • Sink - the interface adapter module accepts DC voltage from the cable. This role is the typical configuration for transmit-side (serializer) interface adapter modules where the remote end provides power.

PoC Source (Powering Remote Devices)

When an interface adapter module operates as a PoC source, it applies a regulated DC voltage onto the coax cable. This voltage powers a remote device such as a serializer or camera without requiring a separate power connection.

Two PoC supply options are available.
  • Internal 12 V source - the carrier module provides a regulated 12 V supply derived from its internal power rail. No external wiring is required.
  • External source - an external supply connected to the carrier auxiliary connector routes to the PoC circuit. The accepted input range is 5 V to 30 V. This range allows you to select a supply voltage appropriate for the remote device.
The PoC source selection and enable state are configurable through the carrier FPGA I/O interface. Setting the source to None (disabled) removes the DC supply from the cable. Setting to None also allows the stored energy in the inductive filters and cable capacitance to dissipate.

PoC Sink (Transmit Use Cases)

An interface adapter module that is operating as a PoC sink receives DC power from the cable supplied by the remote end. This setup is typical for transmit-side interface adapter modules, or serializer role. In this setup, the system at the far end supplies power over the coax cable. The system at the far end typically includes a camera ECU or test head.

In this configuration, the interface adapter module does not supply voltage. The interface adapter module routes incoming PoC voltage from the coax cable to the carrier module auxiliary connector. This routing makes the power available to the test system.

Hot-Plug and Safe Disconnect

GMSL and FPD-Link standards do not support hot-plug or hot-disconnect.
Notice Do not connect or disconnect the coax cable while PoC voltage or stored energy is present. Doing so might damage the interface adapter module or the remote device.
Perform the following procedure before you disconnect the cable.
  1. Disable the PoC source.
    • When operating in source mode, set the source to None.
    • When operating in sink mode, ensure that you disable the remote source.
  2. Wait until the cable has discharged to a safe voltage level before you physically disconnect the cable.
The amount of time required to reach a safe state depends on the stored energy in the system. The time varies between interface adapter module and remote device combinations.

Wait for PoC Safe to Disconnect

The FlexRIO LabVIEW Host API includes a Wait for PoC Safe to Disconnect function. This function monitors the PoC voltage on specified channels and blocks until the voltage falls under a safe threshold. This eliminates the need to estimate or hard-code a fixed discharge delay.

Wait for PoC Safe to Disconnect accepts a channel list and a timeout parameter. A timeout of -1 causes the function to wait indefinitely. A positive timeout value in milliseconds limits the wait and returns a timeout error. The function identifies any channel that did not reach a safe state within the allotted time.

Note For complete API documentation and parameter descriptions, refer to the Wait for PoC Safe to Disconnect VI section in the FlexRIO LabVIEW API Reference.

Support in FlexRIO Interface Adapter Modules

Table 29. PoC Support per Interface Adapter Module
Interface Adapter Module Model PoC Support
IVN-14811 Not supported