ProSoft Technology MVI56-PDPMV1 - Manual (Page 21)

MVI56-PDPMV1 ♦ ControlLogix Platform Start Here
PROFIBUS DPV1 Master User Manual
ProSoft Technology, Inc. Page 21 of 255
March 22, 2011
LEGACY mode offers these advantages:

Works with all module firmware versions; use LEGACY mode for backward
compatibility in older applications.

Since all parameters are fixed, configuration is simpler than FLEX mode.

Status data is bought across the backplane as I/O data without the need for
additional logic to trigger MSG instructions.
FLEX mode implements the following features:

Supports variable backplane I/O block sizes (input backplane block size can
be set from 12 words to 250 words; output backplane block size can be set
from 5 to 248 words).

Status, Slave Diagnostic, and Mailbox data transferred through MSG
instructions.

Supports IOT instruction for immediate write of backplane output.
When transfer speed for smaller data configurations is a priority or when
backward compatibility is not required, consider using FLEX mode, which
provides these advantages:

Makes it easier to support installing the module in a remote rack. The flexible
backplane I/O block size allows you to adjust the amount of data to transfer
for any specific remote rack application and optimize network bandwidth
utilization.

Improves backplane I/O block transfer performance by implementing MSG
instructions to retrieve module status. This means regular I/O block transfers
are not needed for status data, so process I/O data can be updated more
often. The same applies to Mailbox MSG data transfers.

Improves backplane performance by implementing the IOT instruction for
Immediate Output Transfers, which overrides the module RPI time and sends
data as fast as possible.