Chapter 3
Connecting the Signals
DAQCard-1200 User Manual
3-22
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Connecting Analog I/O and General-Purpose Timing Signals
Pins 38 through 48 of the front connector are connections for timing
I/O signals. The DAQCard-1200 timing I/O uses two 82C53 counter/timer
integrated circuits. One circuit, designated 82C53(A), is used exclusively
for DAQ timing, and the other, 82C53(B), is available for general use.
You can use pins 38 through 40 and pin 43 to carry external signals for
DAQ timing in place of the dedicated 82C53(A). These signals are
explained in the next section,
Analog Input Timing Connections
. Pins 41
through 48 carry general-purpose timing signals from 82C53(B). These
signals are explained in the
General-Purpose Timing Connections
section.
Analog Input Timing Connections
Each 82C53 counter/timer circuit contains three counters. Counter 0 on the
82C53(A) counter/timer, referred to as A0, is a sample-interval counter in
timed A/D conversions. The sample interval counter, or channel clock,
controls the time between A/D conversions. A sample interval is also
referred to as the interchannel delay. Counter 1 on the 82C53(A)
counter/timer, referred to as A1, is a sample counter in timed A/D
conversions. Therefore, counter A1 stops data acquisition after a
predefined number of samples. These counters are not available for
general-purpose use.
Counter B1 is a scan-interval counter in timed A/D conversions. The
scan-interval counter, or scan clock, controls the time between when the
first channel in the scan is sampled and when that channel is sampled again.
When the scan-interval counter is used in conjunction with the sample
interval counter, this is referred to as interval scanning. For a more
complete description of interval and round-robin scanning, refer to
Figure 3-12.
Figure 3-12.
Interval Scanning and Round-Robin Scanning
Interval Scanning
Round-Robin Scanning
0 1 2 3
Interchannel Delay
Scan Interval
0 1 2 3
0 1 2 3
0
0
0
1
1
1
2
2
2
3
3
3
Interchannel Delay
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