40
•
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
Summary of Contents for ACL-8112 Series
Page 1: ...NuDAQ ACL 8112 Series Enhanced Multi Functions Data Acquisition Cards User s Guide ...
Page 4: ......
Page 40: ...32 Registers Format 1 1 1 1 1 000 Unipolar N A Table 4 2 1 Function of the Gain Control Bits ...
Page 44: ...36 Registers Format Base 14 DO15 DO14 DO13 DO12 DO11 DO10 DO9 DO8 ...
Page 46: ...38 Registers Format Base 2 Counter 2 Register R W Base 3 8254 CONTROL BYTE ...
Page 71: ...C Language Library 63 ...
Page 81: ...C Language Library 73 Example See Demo Program AD_Demo4 C ...
Page 85: ...C Language Library 77 ERR_AD_INTNotSet Example See demo program AD_Demo2 C ...
