Chapter 3
Connecting Signals
©
National Instruments Corporation
3-15
Caution
Connections, including power signals to ground and vice versa, that exceed
any of the maximum signal ratings on the DAQCard-700 can result in damage to the
DAQCard-700 card. NI is
not
liable for any injuries or damage resulting from incorrect
signal connections
Connecting Timers
Pins 38 through 48 of the I/O connector are connections for TIO signals.
The DAQCard-700 TIO uses an MSM82C54 counter/timer integrated
circuit. All three integrated counter/timers of the MSM82C54 are available
at the I/O connector. One of these counters, counter 0, is used for DAQ
timing. Pin 40 carries an external signal, EXTCONV*, that can be used
for DAQ timing in place of counter 0 of the MSM82C54. This signal is
explained in the
Data Acquisition Counter and Timing Connections
section. Pins 38 and 41 through 48 carry general-purpose timing signals
from the MSM82C54. These signals are explained under the
General-Purpose Counter and Timing Signal Connections
section.
Data Acquisition Counter and Timing Connections
Counter 0 on the MSM82C54 is used as a sample-interval counter in
timed A/D conversions. In addition to counter 0, you can use pin 40,
EXTCONV*, to externally time conversions. Figure 3-7 shows the timing
requirements for the EXTCONV* input. An A/D conversion is initiated by
a rising edge on the EXTCONV*. The data from this conversion is latched
into the FIFO memory within 10
µ
s. The EXTCONV* input is a
TTL-compatible signal.
Figure 3-7.
EXTCONV* Signal Timing
Notice that EXTCONV* only causes conversions to occur; you cannot use
it as a monitor to detect conversions caused by the onboard sample-interval
timer.
A/D Conversion Starts Here
200 ns Minimum
EXTCONV*
V
IH
V
IL
int
