adc-44d ETC-unknow, adc-44d Datasheet - Page 58

• Manufacturer Part Number: adc-44d
• Description: Multi-function Analogue Input/output Card
• Manufacturer: ETC-unknow

Page 50
How to Use DMA
Appendix C
APPENDIX C - HOW TO USE DMA
Direct Memory Access or DMA is a process by which data can be transferred
directly from the memory of the PC into an I/O card or directly from the I/O
card into the PC memory with no intervention from the processor. This can
greatly increase the throughput of data and at the same time, reduce the
overhead of processor time.
The DMA Controller
DMA is controlled by the PC using one of two DMA Controllers. The DMA
Controllers are INTEL i8237 or compatible devices, each containing four
channels. The first one is used for byte transfers in the bottom 1 MB of system
memory, the second can transfer words into the bottom 16 MB.
Blue Chip Technology boards only allow DMA channels 1 or 3 on the first
controller to be used. Normally channel 0 is reserved for memory refresh
control and channel 2 is used by the floppy disk drives.
In order to begin a DMA transfer, first the I/O board must be configured to
enable DMA operation - consult the relevant section of the manual on how to do
this. Secondly, the DMA controller must be programmed to begin the transfer.
The DMA controller is programmed by writing to I/O ports in much the same
way as the card is programmed.
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Blue Chip Technology Ltd.