Chapter 2
Configuration and Installation
© National Instruments Corporation
2-37
AT-MIO-16D User Manual
The pulse is typically 200 nsec in width. The EXTSTROBE* signal can be used by an external
device to latch signals or trigger events. The EXTSTROBE* signal is an LS TTL signal.
A/D conversions can be externally triggered with the EXTCONV* pin. Applying an active low
pulse to the EXTCONV* signal initiates an A/D conversion. The A/D conversion is initiated by
the low-to-high edge of the applied pulse. Figure 2-34 shows the timing requirements for the
EXTCONV* signal.
t
w
50 nsec minimum
A/D conversion starts within
250 nsec from this point
V
IL
V
IH
t
w
t
w
Figure 2-34. EXTCONV* Signal Timing
The minimum allowed pulse width is 50 nsec. An A/D conversion starts within 250 nsec of the
low-to-high edge. There is no maximum pulse width limitation. EXTCONV* should be high for
at least 50 nsec before going low. The EXTCONV* signal is one LS TTL load and is pulled up to
+5 V through a 4.7-k
Ω
resistor.
Note: EXTCONV* is also driven by the output of Counter 3 of the Am9513A Counter/Timer.
This counter is also referred to as the sample-interval counter. The output of Counter 3
must be disabled to a high-impedance state if A/D conversions are to be controlled by
pulses applied to the EXTCONV* pin. If Counter 3 is used to control A/D conversions,
its output signal can be monitored at the EXTCONV* pin.
You can initiate any data acquisition sequence controlled by the onboard sample-interval and
sample counters by an external trigger applied to the START TRIG* pin. If conversions are
generated by the EXTCONV* signal, START TRIG* does not affect the acquisition timing. Once
the two counters are initialized and armed, applying a falling edge to the START TRIG* pin starts
the counters, thereby initiating a data acquisition sequence.
The data acquisition operation is initiated by the high-to-low edge of the applied pulse. Figure 2-35
shows the timing requirements for the START TRIG* signal.
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