Advantech PCL-848A/B Manuel d'utilisateur télécharger pdf (Page 59)

CHAPTER 5

ADVANCED PROGRAMM1N TECBNIQUES

The DMA operation of this IEEE-488 interface is quite transparent to users. Once

you select the DMA mode by calling INIT routine, all further data transfer proceeds

in this mode. Bowever, when you select block-transfer mode, the DMA channel 0

memory refresh may be held long enough to corrupt RAM memory content. Do not

use block-transfer mode unless you have confidence that the data transfer will be

completed within the time limits of memory refresh.

When using background operation, the CPU does not care about the data transfer. The

data string can be terminated by byte count only. The data format problem then must

be handled by users. It is safe to use DMA in single-byte-transfer and non-back-

ground operation mode (the default condition). The other modes can be used only

when you have solid understanding of the PC, 8237 DMA chip and your IEEE-488

devices. We do not recommend using these modes.

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Advantech PCL-848A/B Manuel d'utilisateur Page 59