Clock Selection; Figure 2-6. Jumper J2 Configuration - Omega Engineering DAQ-16 User Manual

2.5

Clock Selection

The DAQ-16 is equipped with a programmable clock circuit to produce data sampling rates
independent from the clock rate of the host computer. An onboard 8254 programmable
interval timer, with a 10 MHz clock input and either two or three cascaded 16-bit timers,
provides the sampling rate. This enables the sampling rate to be adjusted from 10 us between
samples to almost a year between samples, in as small as 100ns increments.
The DAQ-16's sampling rate can also be generated from an external clock input. This external
clock can be connected directly to the A/D converter or through a 16-bit pre-divider, the
multi-function timer. Samples are taken on the low to high transition of the clock.
WARNING: For the DAQ-16, the maximum data sampling rate is 10 us. This restricts
clock frequency to a maximum of 100 KHz. Sampling rates in excess of 100 KHz may
The clock source, internal or external clock, is software selectable through the DAQ-16's
control word register. The configuration of the clock source itself is controlled by jumper
block J2 as shown in Figure 2-6, (* indicates factory default).
DAQ-16 Users Manual
result in erratic operation and unpredictable results.
J2
5 6 7 8
1 2 3 4

Figure 2-6. Jumper J2 Configuration

Internal Timer: 2 timers cascaded
connect 1-2, 6-7*
3 timers cascaded
connect 2-6, 7-8
External Timer: w/o pre-divider
connect 1-2, 3-4
with pre-divider
connect 2-3, 4-8
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