NuDAQ ACL-8112 Series, Руководство пользователя

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Operation Theorem
5.1.2 A/D Trigger Modes
In the ACL-8112, A/D conversion can be triggered by the Internal or
External trigger source. The jumper JP5 is used to select the internal or
external trigger, please refer to section 2.8 for details. Whenever 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-8112.
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 is starting 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 is occurred. 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.
5.1.3 A/D Data Transfer Modes
On the ACL-8112, three A/D data transfer modes can be used when the
conversion is completed. The data transfer mode is controlled by the