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AD1200 Reference
converter in the background whilst the computer is apparently
busy doing another job. DMA is ideal for moving large amounts
of data very quickly. The DMA hardware requires that the DMA
channel jumper settings should be set for DMA operation to be
performed. The AD1200 board is designed so that it will only
generate DMA requests when the DMA enable bit, bit 3, in the
control status register, is set. When the DMA enable bit is clear,
0 the DMA request line is tristated off, the AD1200 card cannot
perform DMA i/o and does not drive the DMA channel lines at
all. This allows for DMA line sharing.
The position of the DMA channel jumper MUST match the
DMA channel used in the software. The range of instructions
controlling the enabling and use of the DMA facility are
described in later chapters.
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Setting The DMA Channel Jumper Block.
Only the AD1200 card can perform DMA driven i/o. Two
movable jumpers on the DMA jumper block, DMAJMP, are
used to select the channel through which the direct memory
access transfers pass.
Most user will not require DMA and so should leave the
DMA jumpers in the factory set position, DMA 1.
One of the jumpers is across the DMA request line and the
other across the DMA acknowledge line. Moving the jumper
pins select which DMA channel is invoked by the AD1200
board hardware. The jumpers can be in one of three positions,
see Figure 2-9. The jumpers must be set in pairs, both jumpers
MUST be set in the same DMA channel pair.
NOTE: Do not add an extra jumpers of your own across the
jumper block, it will only cause great confusion.
Page 36
Installation Guide
AD1200 Only
Chapter 2
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