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John User

GPIO, 1PPS, and Ref features


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These are interfaces for which hardware has been integrated but require additional firmware implementation to enable them.  This capability will be available in a future software release.

The GPIO (general-purpose, input-output) interface on the WBT consists of four 5-volt, TTL lines on a 6-pin, RJ12 jack.  The signals on the lines are defined by a custom, embedded application as either inputs or outputs to provide an application-specific interface to provide features such as as antenna switching, COR (carrier-operated relay) status, audio squelch, transmitter blanking, or to pass event signals to/from external processes.

The WBT REF (reference) connector may be configured as either input or output to synchronize the frequency accuracy of the WBT's internal local oscillator and ADC sample clock with one or more external resources (e.g., other WBT's or test equipment like a signal generator).  When the port is configured as an output the connector provides a 2.5 Vpp , 10 MHz sine wave with an optimal load of 50 ohms.  The ideal reference input signal is also 2.5 Vpp.  The WBT has an extremely accurate oven-controlled, crystal oscillator (OXCO); without conditioning the accuracy is 25 ppb, with GPS conditioning it's 10 ppb.

The 1PPS connector (one pulse-per-second) provides a signal used to synchronize events like starting a data stream and things like time-stamp clocks.  A 1PPS signal may originate in a GPS receiver and is commonly available from an IRIG receiver.  It may be distributed to multiple devices to synchronize a system.  When the WBT 1PPS port is configured as an output, the signal is a 3.3V CMOS logic signal that goes high for 200 ms every second.  The rising edge indicates a 1PPS clock tick from the internal GPS or a free-running clock.

When the ports are configured as outputs, the WBT is the master or source of both the REF and 1PPS signals.  

When the ports are configured as inputs, the WBT uses the external signals to drive it's LO and ADC sample clock, and to synchronize data stream starts.

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These connectors serve the following purposes:

GPIO - GPIO Pins which will, in a future software / API release, allow the user to detect and send voltage changes to another connected device (such as an antenna switcher or an alarm)

1PPS / REF -  In a future software / API release, these connectors will allow clock distribution to or from the WBT into other devices which  rely on or supply signals required for accurate, coordinated timing.

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