Measurement Computing USB-1608HS - Manual (Page 19)

USB-1608HS User's Guide Functional Details
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SYNC terminals (SYNC_IN and SYNC_OUT)
You can use the SYNC_IN connection to externally pace the A/D conversions. The SYNC_IN terminal supports
TTL-level input signals of up to 250 kHz.
Use the SYNC_OUT connection to output the clock used for A/D conversions.
One example of the use of these two pins would be to synchronize with a second USB-1608HS and acquire
synchronized data from 16 channels. You can connect the
SYNC_OUT pin of one USB-1608HS to the
SYNC_IN pin of another USB-1608HS to acquire data synchronously from 16 channels.
Figure 10. Configuring for synchronous data acquisition
Trigger terminal (TRIG_IN)
The TRIG_IN connection is an external analog/digital trigger input.
With the analog trigger function, you can start and control acquisitions with an analog signal. The analog trigger
threshold is from -10 V to +10 V on the TRIG_IN pin. A 12-bit DAC sets the level for the threshold. The
threshold resolution in this mode is 4.88 mV.
The USB-1608HS has three trigger options that you must set.
 Trigger above or trigger below
 Level-sensitive or edge-sensitive
 Retrigger on or retrigger off
Each trigger operation mode is explained next. In each case, a ±2 V triangle waveform is used as the TRIG_IN
input source. The high threshold is set to 1.0 V, and the low threshold signal is set to -1.0 V.
In the following analog trigger signal diagrams, the bold portion of the waveform indicates the data acquired for
the given analog trigger mode.
SYNC_IN pin
SYNC_OUT pin