Measurement-computing GPIB-488 Uživatelský manuál stáhnout pdf (Strana 30)

Chapter 3 GPIB 488.1 Library Reference

GPIB-488 3-17 Programming Reference Manual

IBDMA

Enables/Disables DMA.

Syntax

C ibdma (int board, int dma)

Parameters

board is an integer containing the board handle.

dma is an integer which indicates whether DMA is to be enabled or disabled for the specified

GPIB board. If

dma is non-zero, all read and write operations between the GPIB board and

memory are performed using DMA. Otherwise, programmed I/O is used.

Returns

ibsta will contain a 16-bit status word as described in Appendix B, IBSTA.

iberr will contain an error code, if an error occurred. An ECAP error results if you tried to

enable DMA operations for a board which does not support DMA operation. If no error

occured, the previous value of

dma is stored in iberr.

Usage Notes

The GPIB Interface Board must have been configured for DMA operations in order for this

routine to be executed successfully. This routine is useful for alternating between

programmed I/O and DMA operations. This call remains in effect until one of the following

occurs:

• Another

ibdma call is made.

•

ibonl or ibfind is called.

• The program is re-started.

• The maximum DMA transfer length in Windows is 64 K bytes.

Example

This example enables DMA transfers for GPIB Interface Board 1. It

assumes that the DMA channel was previously selected in your

configuration program.

C int board, ibsta;

board = ibfind ("gpib1");

ibsta = ibdma (board, 1);

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