Data Translation DT3000 Series, User Manual, Page: 78 / 156

Principles of Operation
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Trigger Sources
A trigger is an event that occurs based on a specified set of conditions. DT3000 Series boards
support the following trigger sources:
• Software trigger – A software trigger event occurs when you start the analog input
operation (the computer issues a write to the board to begin conversions). Specify the
software trigger source in software.
• External digital (TTL) trigger – For analog input operations, an external trigger event
occurs when the DT3000 Series board detects either a rising or falling edge on the external
trigger input signal connected to TB6 on the DT730 or DT730-T screw terminal panel (pin
6 of connector J1 on the DT3000 Series board). The trigger signal is TTL-compatible.
The trigger pulse is recognized when it is of the correct polarity and has a pulse width
greater than 500 ns. When it is recognized, the A/D sample clock is enabled. Subsequent
triggers are ignored (trigger lockout) until the operation is complete. Once the operation is
complete, the board can detect another trigger.
Using software, specify the trigger source as an external, positive digital (TTL) trigger for
a rising-edge external trigger or an external, negative digital (TTL) trigger for a
falling-edge external trigger.
Note: The external digital trigger is also used to trigger analog output operations.
Data Format and Transfer
DT3001, DT3001-PGL, DT3002, DT3003, and DT3003-PGL boards use offset binary data
encoding to represent bipolar signals. DT3004 and DT3005 boards use twos complement data
encoding to represent bipolar signals. Use software to specify the data encoding type.
The board is mapped into memory space to allow the use of the multiple read bus instruction.
The data transfer starts when a user-defined number of samples has accumulated. The
accumulated sample data is stored in an onboard circular buffer, which is accessible for read
operations by the host computer. An interrupt is sent to the host computer, notifying it with a
message indicating that sample data is ready to be read. The host computer then commands
the PCI bus master to transfer the sampled data from the onboard buffer to its destination in
memory. Digital samples are received from the 12-bit A/D section and are sign-extended to 16
bits.
The DT3000 Series Device Driver accesses the onboard circular buffer to fill user buffers that
you allocate in software. It is recommended that you allocate a minimum of two buffers for
analog input operations and add them to the subsystem queue using software.
Data is written
to the queued input buffers continuously; when no more empty buffers are available on the
queue, the operation stops. The data is gap-free.
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