Rockwell Automation 1756-DNB ControlLogix DeviceNet Scanner Module Installation Instructions - Manual (Page 38)

38 ControlLogix DeviceNet Scanner Module
Publication 1756-IN566D-EN-P - June 2008
Understand ControlLogix Controller Interface Structures
The 1756-DNB scanner module supports several sizes of input, output, and
status structures over the ControlLogix backplane. These I/O structures were
created to reduce the complexity of connecting DeviceNet I/O and status
data with ladder programs.
The module creates all three structures whether DeviceNet devices are
configured or online.
RSLogix 5000 software directs the controller to connect to these predefined
default I/O structures. The controller automatically performs periodic
updates of the structures on a cyclic basis.
RSNetWorx for DeviceNet software configures scanlist map segments that
are used to copy specific portions of I/O data between the I/O structures
and DeviceNet network packets.
Output Structure
The controller controls output I/O by writing output data to an output
structure in the 1756-DNB scanner module. The scanner module then
delivers a copy of these output values to modules on DeviceNet. The output
structure consists of a 32-bit command register and a variable size 32-bit array
of up to 123 words for output data.
IMPORTANT
Only one Logix controller at a time can send outputs to the 1756-DNB
scanner module.
Output Structure Element Description Data Type
module command register This 32-bit register consists of
several bits that affect the module’s
behavior on the network. 1 x 32-bit register
output_data 123 x 32-bit data array