Rockwell Automation 1747-BSN Backup Scanner Module - Manual (Page 24)

Publication 1747-UM010B-EN-P - September 2003
1-10 Overview
Through your control program you command the SLC processor to
initiate RIO block transfers, which directs the scanner to exchange
large amounts of data to/from an adapter. Block Transfers (BTs) use
the basic RIO discrete transfer mechanism of the RIO link. However,
the actual transfer of data occurs asynchronous to the discrete
transfers. It is possible for several discrete transfers to occur before the
scanner processes a block transfer. Refer to Chapter 7, RIO Block
Transfer for more details.
Physical and Logical RIO Link Specifications
The maximum number of adapters with which your scanner can
communicate is determined by the scanner’s and adapter’s physical
and logical specifications, as described below:
•
Physical Specifications are the maximum number of adapters
that can be connected to the scanner. For more information, see
Extended Node Capability below.
•
Logical Specifications for the scanner are the maximum number
of logical racks the scanner can address, how the logical racks
can be assigned, and whether the scanner can perform block
transfers.
Extended Node Capability
Extended node functionality allows you to connect up to 32 physical
devices on an RIO link. You must use 82 Ohm termination resistors in
an extended node configuration. You can only use extended node if
all RIO link devices have extended node capability. (Refer to the
Compatible Devices table at the end of this chapter, or to the
specifications of your device.) The 1747-BSN scanner has extended
node capability. However, the smallest logical rack division is 1/4
logical rack and the scanner image size is 4 logical racks. Therefore,
the scanner is limited to 16 devices unless complementary I/O is used.
Refer to the following section for more information on complementary
I/O.
Complementary I/O Complementary I/O is very useful when portions of your input and
output images are unused because it allows the images of two
adapters to overlap each other in the scanner’s I/O image. To use
complementary I/O, the I/O image from one adapter must be the
mirror (complement) of the other. This means that if there is an input
module in the primary chassis, there must be an output module in the