Chapter 2
Hardware Configuration and Installation
© National Instruments Corporation
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VXI-AT2000/NI-VXI MS-DOS Getting Started
memory protocol that uses the PC AT memory, you must select and enable a slave-mode DMA
channel. However, because the AT-MXI does not share resources in its default software
configuration, you need to change some software settings before you can use this feature. Refer
to the Logical Address Configuration section of Chapter 3,
NI-VXI Software Installation and
Configuration, to see the default settings of the fields that affect the slave-mode DMA channel.
The default settings are as follows:
•
The Address Space field is set to A16 only. To share RAM you need to change this field to
A16/A24.
•
The VXI Shared RAM Window Size field is disabled. To share RAM you need to assign a
value in the allowable range.
•
The Slave I/O Window Size field is disabled. To share I/O space you need to assign a value
in the allowable range.
•
The Slave DMA Channel field is set to use channel 3, which is acceptable. If you modified
this field to the NONE setting, slave accesses to shared RAM in VXI space and PC I/O space
would not succeed. You could assign a NONE setting to this field if you intend to keep the
three settings described above in their default settings. This change would free up the DMA
channel for use by other devices in the system. On the other hand, if you ever need to switch
back and forth between A16 and A24 space, it would be easier to have a slave DMA channel
already reserved for the AT-MXI, and just change the appropriate settings in
VXIEDIT
.
Remember that the hardware and software settings must match if you intend to use a slave
DMA channel.
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.
