Tektronix 2212 Service Manual page 101

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