Triggers
2-13
Once the board is armed, the next valid trigger event starts the acquisition.
When the trigger event occurs, the post-trigger length, which includes the
post-trigger delay and the number of samples to acquire (defined by the
buffer length), is decremented until it reaches zero, at which point
acquisition stops. Using software, you can poll a status bit or use an
interrupt to determine if the acquisition is finished.
For example, assume the conversion rate is 50 Msample/s, the
post-trigger delay is 10 samples and the buffer length is 190 samples.
When a valid trigger event occurs, the first 10 samples are ignored, the
remaining 190 post-trigger samples are collected, then the acquisition
operation stops.
About-Trigger Acquisition
Use about-trigger acquisition to store data samples before a trigger event
occurs or before and after a trigger event occurs.
To start an about-trigger acquisition, perform the following steps:
1. Set up all board parameters, such as the data acquisition channel,
voltage input range, conversion rate, trigger source, trigger polarity,
and the number of samples to acquire after the trigger occurs. You
need to set up these parameters only once unless your application
requires a change.
2. Using software, arm the board to accept the next valid trigger event.
Arming the board requires about 10
µ
s.
Once armed, the board continuously acquires data and stores it in the
onboard 8K byte memory buffer. The memory buffer must fill up with
data at least once before the board can accept a trigger event. When a
valid trigger event occurs, the specified number of post-trigger samples
(defined by the buffer length) is collected.
For example, suppose you set the buffer length to 4,160 and start the
about-trigger operation. Pre-trigger data is collected and begins to fill the
8K byte buffer. Once the buffer is filled, the board can accept a trigger;
pre-trigger data continues to be collected and overwrites the data in the
buffer until the trigger event occurs. When a valid trigger event occurs,
the board collects 4,160 post-trigger samples then stops the acquisition.
The number of pre-trigger samples in the buffer is 8,192 minus 4,160 or
4,032.
Summary of Contents for DAS-4300 Series
Page 1: ...DAS 4300 Series U S E R S G U I D E...
Page 2: ...DAS 4300 Series User s Guide Revision A June 1995 Part Number 94520...
Page 21: ...2 6 Functional Description Figure 2 2 Host Computer Memory Address Space...
Page 90: ...C 9 Figure C 16 0 125 V Input Range Gain Code 15 0 125 V Input Range Gain Code 15...
