ADLINK ACL-8216 - Manual (Page 42)

34 • Operation Theorem
The A/D data should be transferred into PC's memory for further using. The
ACL-8216 provides three data transfer modes that allow users to optimize
the DAS system. Refer to section 5.1.3 for data transfer modes.
4.1.2 A/D Trigger Modes
In the ACL-8216, A/D conversion can be triggered by the Internal or External
trigger source. The jumper JP4 is used to select the internal or external
trigger, please refer to section 2.8 for details. henever the external source is
set, the internal sources are disable.
The two internal sources are the software trigger and the timer pacer trigger
which is controlled by the A/D operation mode control register (BASE+11).
Total three trigger sources are possible in the ACL-8216. The different trigger
conditions are specified as follows:
Software trigger
The trigger source is software controllable in this mode. That is, the A/D
conversion starts when any value is written into the software trigger register
(BASE+12). This trigger mode is suitable for low speed A/D conversion.
Under this mode, the timing of the A/D conversion is fully controlled under
software. However, it is difficult to control the fixed A/D conversion rate
except another timer interrupt service routine is used to generate a fixed rate
trigger.
Timer Pacer Trigger
An on-board timer / counter chip 8254 is used to provide a trigger source for
A/D conversion at a fixed rate. Two counters of the 8254 chip are cascaded
together to generate trigger pulse with precise period. Please refer to section
5.4 for 8254 architecture. This mode is ideal for high speed A/D conversion.
It can be combined with the DMA or the interrupt data transfer. It's
recommend to use this mode if your applications need a fixed and precise
A/D sampling rate.
External Trigger
Through the pin-17 of CN3 (ExtTrig), the A/D conversion also can be
performed when the a rising edge of external signal occures. The conversion
rate of this mode is more flexible than the previous two modes, because the
users can handle the external signal by outside device. The external trigger
can combine with the DMA transfer, interrupt data transfer, or even program
polling data transfer. Generally, the interrupt data transfer is often used
when external trigger mode is used.