DMA Transfer (DMAX)

The DMA (Direct Memory Access) bus master allows data to be transferred directly between the PCI-9112 and the PC memory at the fastest possible rate, without using any CPU time. The A/D data will be queue at local FIFO on the PCI-9112 itself and it is automatically transferred to PC's memory.

The DMA transfer mode is very complex to program. It is recommended to use the high level program library to operate this card. If you wish to program the software which can handle the DMA bus master data transfer, please refer to more information about PCI controller.

4.3D/A Conversion

The operation of D/A conversion is more simple than A/D operation. You only need to write Digital values into the D/A data registers and the corresponding voltage will be output from the AO1 or AO2. Refer to

section 4.3 for information about the D/A data registers. The mathematical relationship between the Digital number DAn and the output voltage is formulated as following:

Vout = −Vref ×

DAn

4096

where the Vref is the reference voltage, the Vout is the output voltage, and the DAn is the Digital value in D/A data registers.

Before performing the D/A conversion, users should care about the D/A reference voltage which set by the JP3 and JP4. Please refer section 2.8 for jumper setting. The reference voltage will effect the output voltage. If the reference voltage is -5V, the D/A output scaling will be 0~5V. If the reference voltage is -10V, the D/A output scaling will be 0~10V.

The PCI-9112 has two unipolar analog output channels. To make the D/A output connections from the appropriate D/A output, please refer Figure 3.8.

-5 or -10 INT or Ext

Ref In

D/A Converter

Pin-30 ( AO0)

Pin-32 ( AO1)

-

+

ToD/A Output

 

Pin-14 ( A.GND)

Analog GND

Figure 4.3 Connection of Analog Output Connection

Operation Theorem ∙ 33