2212 Service Manual
Long
Record Option
The DMA (Direct Memory Access) process of transferring acquisition data to
the microprocessor has basically remained the same. Because the internal
~
DMA controller of the 68070 has a maximum transfer count of 64K
-1,
the
transfer oflarge datablocks
for
record-lengths of 64K
and
up, is performed
in
blocks
of
32K.
Therefore, the transfer is done
in
burst mode. The REQ2_0 input
of the 68070 is made level sensitive instead
of
edge sensitive. Changing from
edge sensitivity to level sensitivity required some
minor
changes
in
the
OMA
handshake circuitry (see Diagram 16A).
Revised 3/93
3-43
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