National Instruments VXI-AT2023 Getting Started page 19

Chapter 2
The DMA jumpers are set at the factory with the master-mode interface set to DMA channel 6 and
enabled by the default configuration software. The slave-mode interface is set to DMA channel 3.
The default configuration software disables the slave-mode interface circuitry so that, even though
the slave-mode DMA is jumpered to channel 3, the board does not use this level unless you make a
change to the software configuration.
Note: Seldom, if ever, can the AT-MXI share DMA channels with other devices. If you have
selected a DMA channel by placing jumpers on that channel's request and acknowledge
lines and enabled the channel in software, no other devices in your system should use
that channel. If DMA channels conflict, change the DMA channel(s) used by either the
AT-MXI or the other device(s). If you change an AT-MXI DMA channel, make a
corresponding change to the AT-MXI configuration software as described in the
Configuring the NI-VXI Software section of Chapter 3.
The AT-MXI can use DMA Channels 0, 1, 2, 3, 5, 6, and 7. Be careful when reassigning DMA
channels on the AT-MXI. Notice that most PC ATs use DMA Channel 2 for the disk controller
interface. It is possible that various standard logic devices on the motherboard may use other DMA
channels, so check your computer documentation before changing DMA channels.
Notice that the PC AT makes a distinction between 8-bit and 16-bit DMA channels. The 8-bit
channels are 0, 1, 2, and 3. The 16-bit channels are 5, 6, and 7. The master-mode DMA channel
setting must match the data width of the intended block transfers. It is preferable to use one of the
16-bit channels for the master-mode interface because a 16-bit DMA channel can transfer twice the
amount of data in the same number of cycles. The slave-mode DMA channel is used only to
request the PC AT bus for an alternate PC AT bus master cycle. It can use any available 8-bit or
16-bit channel regardless of the intended data width of the transfers.
Use the two rows of pins farther from the card-edge connector to select the master-mode DMA
channel and the two rows closer to the card-edge connector to select the slave-mode DMA channel.
Remember that the jumper positions should be identical on both the W1 and W2 arrays. Figure 2-
4a shows the factory default DMA channel setting of the AT-MXI, with master-mode DMA
Channel 6 and slave-mode DMA Channel 3.
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Hardware Configuration and Installation
2-9 VXI-AT2023/NI-VXI ISC 386/ix Getting Started