National Instruments GPIB-PC - page 100

Section Four A BASICA/QuickBASIC GPIB-PC Function Calls
©National Instruments Corp. 4A-25 GPIB-PC User Manual
BASICA/QuickBASIC BASICA/QuickBASIC
IBDMA IBDMA
Purpose: Enable or disable DMA
Format: CALL IBDMA (BD%,V%)
Remarks: BD% specifies an interface board. If V% is non-zero, DMA
transfers between the GPIB-PC and memory are used for
read and write operations. If V% is zero, programmed I/O is
used in place of DMA I/O.
If you enabled DMA at configuration time, assigning DMA
channel 1, 2, or 3, this function can be used to switch
between programmed I/O and DMA using the selected
channel. If you disabled DMA at configuration time,
calling this function with V% equal to a non-zero value
results in an ECAP error.
The assignment made by this function remains in effect
until IBDMA is called again, the IBONL or IBFIND
function is called, or the system is rebooted.
When IBDMA is called and an error does not occur, the
previous value of V% is stored in IBERR%.
On machines without DMA capability, calling this function
with V% = 0 has no effect, and calling it with a non-zero V%
results in an ECAP error.
Refer also to Table 2.1.
Board Examples:
1. Enable DMA transfers using the previously configured channel.
100 V% = 1 ' Any non-zero value will do.
110 CALL IBDMA (BRD0%,V%)
2. Disable DMAs and use programmed I/O exclusively.
100 V% = 0
110 CALL IBDMA (BRD0%,V%)