Rockwell Automation 6008-SV2R VMEbus remote I/O Scanner - Manual (Page 46)

Chapter
Communicating with Remote I/O
4
4Ć9
The scanner processes block-transfers differently depending on the VME
operating mode. In general though, block-transfer allows the VME master
processor to read or write up to 64 16-bit words from an adapter.
In SV-compatible mode
The scanner processes single block-transfer operations. You must program
a read or write command for each data transfer in your application. The
scanner can queue as many as 42 block-transfer requests from the VME
master processor.
In SV-superset mode
The scanner processes single block-transfer operations and continuous
block-transfer operations. The single block-transfer operations work the
same as in SV-compatible mode. The only difference is that the scanner
can only queue one request from the VME master processor. Use
continuous block-transfer requests for applications that need to
continuously poll an adapter. The continuous block-transfer requests uses
less overhead than programming a single block-transfer request each time
you need the data.
For specifics on block-transfers based on VME operating mode, see
chapter 5 or 6 for SV-compatible or SV-superset mode, respectively.
Understanding the BlockĆTransfer Sequence
The VME master processor and scanner alternately access the scanner’s
global RAM while transferring a block transfer. See Figure 4.6 and
Figure 4.7.