BNC 630 - Manual (Page 11)

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4.
External Trigger/Gating/FSK/BPSK input
The External Trigger/Gating/FSK In connector accepts an external digital signal on the rear of the unit as illustrated here:
Figure 2.0-4: Driving the Ext Trigger/Gating/FSK/BPSK input
On this connector the user supplies a digital signal which serves a variety of purposes, depending on the operating mode of the
630.
This input is a high impedance input (about 80K ohms) and can safely accept input levels from -10V to +10V. The input uses a
comparator with a switching point of about 1.4V permitting either TTL or CMOS logic to drive this input. The input has hysterisis,
too, so you can apply analog signals to this input (i.e. a sinewave).
This input has an internal pulldown resistor which holds it in the low or "0" state when left open.
In most modes, this input can be used to switch the output signal on or off. When driven high, the output signal is gated off. This
function can be performed up to 3 MHz. When the output is gated off, the DC level on the Sig Out jack is unpredictable. The
Gating input "freezes" the output waveform at the output voltage is held to the voltage value that existed at the moment the Gating
input went high. When the Gating input is brought low again, the output waveform resumes from the same point.
In the External FSK and BPSK modes, this input is used to bring in digital data for FSK or BPSK modulation.
In the Burst and Triggered Sweep modes, this input is used as a trigger signal. Driving this input high triggers a sinewave burst or
starts a sweep.
In the Continuous Sweep mode, the sweep can be halted by driving this input high. The sweep will resume when this input is
brought low again.
In the Arbitrary, Function, and Pulse Generator modes, this input serves as a trigger signal input. If Triggered mode is selected,
the generation of your arbitrary/function/pulse waveform will commence on the rising edge of the trigger signal.
*** Caution ***
Be careful to ensure that the input signal does not exceed the +/- 10V limit. Permanent damage to this input may result by
exceeding this input voltage limit.