Chapter 2
Installation and Configuration
PC/104-GPIB for Windows 95
2-14
©
National Instruments Corporation
Configure the PC/104-GPIB Direct Memory Access
Direct memory access (DMA) refers to data transfers directly to or
directly from devices such as the PC/104-GPIB and system memory.
Your GPIB hardware and software are designed to perform DMA. In
most cases, data transfers using DMA are significantly faster than
programmed I/O transfers, which use more CPU time. However, if
Windows 95 is unable to assign a DMA resource to the PC/104-GPIB,
or if you are installing the PC/104-GPIB in an 8-bit stack, you can
configure DMA to none and still use the GPIB software for
Windows 95. By default, the PC/104-GPIB is configured to use DMA
channel 5.
Note:
If you are installing the PC/104-GPIB in an 8-bit stack, you must disable
DMA, because DMA channels 5, 6, and 7 are 16-bit DMA channels. Refer
to Figure 2-12, which shows how to set the DMA jumpers for no DMA.
Follow these steps to reconfigure the DMA channel.
1.
Locate the jumpers that select the DMA channel. Refer to the parts
locator diagram, Figure 2-7.
2.
Change the jumper settings to configure the PC/104-GPIB to the
DMA channel Windows 95 assigns or to no DMA if you are
installing the PC/104-GPIB in an 8-bit stack.
To select a new DMA channel, you must set both the DMA
Acknowledge and DMA Request lines, as shown in Table 2-3.
Table 2-3. PC/104-GPIB DMA Channel Settings
Signal Lines
DMA Channel
DMA Acknowledge
DMA Request
5
DACK5
DRQ5
6
DACK6
DRQ6
7
DACK7
DRQ7
none
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