Rockwell Automation 20-COMM-R Remote I/O Adapter - Manual (Page 44)

4-8 Using Discrete and Block Transfer I/O
20-COMM-R Remote I/O Adapter User Manual
Publication 20COMM-UM004D-EN-P
drive. If a request has fewer than eighteen words, as much I/O data as will
fit in the request will be used.
Reference/Feedback in Block Transfer I/O Image
Word 0 and word 1 are reserved for the Reference/Feedback. The size of the
Reference (16-bits or 32-bits) is determined by the drive. If a 16-bit
Reference (
Figure 4.3 ) is used, word 1 is not used during writes and is read
as zero (0) during reads.
Important: If the adapter is configured as a 1/2 rack, it uses the Reference
from the Discrete I/O and ignores the Reference in the Block
Transfer I/O. Feedback is transmitted in both Discrete I/O and
Block Transfer I/O.
Datalinks in Block Transfer I/O Image
Words 2 through 17 are optionally enabled for Datalinks. A Datalink is a
mechanism used by PowerFlex drives to transfer data to and from the
controller. Datalinks let a drive parameter value to be read or written
without using an Explicit Message. When enabled, each Datalink occupies
four 16-bit words in both the input and output Block Transfer I/O image.
The size of Datalinks (16 bits or 32 bits) is determined by the drive. If 16-bit
Datalinks (
Figure 4.3 ) are used, the most significant word of each Datalink
is not used during writes and is read as zero (0) during reads.
Rules for Using Datalinks
• Each set of Datalink parameters in a PowerFlex drive can be used by
only one adapter. If more than one adapter is connected to a single drive,
multiple adapters cannot use the same Datalink.
• Parameter settings in the drive determine the data passed through the
Datalink mechanism. Note that some parameters may not be allowed as
Datalinks. See the documentation for your drive.
• When you use a Datalink to change a value, the value is not written to
the Nonvolatile Storage (NVS) memory. The value is stored in volatile
memory and lost when the drive loses power. Thus, use Datalinks when
you need to change a value of a parameter frequently.