Rockwell Automation 6008-SV2R VMEbus remote I/O Scanner - Manual (Page 45)

Chapter
Communicating with Remote I/O
4
4Ć8
A VME master processor then reads the input image information from the
global RAM via the VMEbus.
To generate an output, a VME master processor sets a specific bit in the
I/O image table in the scanner’s global RAM, corresponding to the desired
output device, for example a control relay.
The scanner updates the adapter during the next scan cycle. The adapter
sets the appropriate bit in the output module and the discrete output device
energizes the control relay.
In addition to discrete data, the scanner can also exchange block data with
remote I/O. Block transfers are the communication of data blocks (files)
between the scanner and intelligent I/O modules. These are any I/O
modules that respond to read or write block transfers. These modules
handle data such as analog input, analog output, positioning, and
communication data.
Block-transfer instructs the scanner to transfer as many as 64 words of data
to/from a selected I/O module. The operating mode of the scanner
determines how many block-transfer requests the scanner can queue as
many as 42 requests when operating in SV-compatible mode; only 1
request when operating in SV-superset mode. Figure 4.5 shows how the
scanner handles a block-transfer.
Figure 4.5
BlockĆtransferring data to remote I/O
adapter
adapter
adapter
Rack 3
Rack 2
Rack 1
blockĆtransfer
request VME
master
processor
scanner
block
transfer
table Q
A
Q = queue
A = active
blockĆtransfer
sent to adapter
scanner
Processing Block Data