Rockwell Automation 1769-SDN Compact I/O DeviceNet Scanner Module User Manual - Manual (Page 14)

14 Publication 1769-UM009E-EN-P - August 2009
Chapter 1 Overview
Communication with Your
Slave Devices The scanner module communicates with devices via strobe, poll, change of
state, or cyclic I/O messages. It uses these messages to solicit data from or
deliver data to each device. Data received from the devices, input data, is
organized by the scanner module and made available to the controller. Data
sent from your controller, output data, is organized in the scanner module and
sent on to your devices.
• A strobe message is a multicast transfer of data that is 64 bits in length
sent by the scanner module that initiates a response from each strobed
slave device.
The strobe devices respond with their data, which can be as much as 8
bytes of information. As a slave device, the scanner module does not
support the strobe message.
• A poll message is a point-to-point transfer of data from 0...128 bytes
sent by the scanner module to the slave device.
The poll message also initiates a response from each poll slave. The slave
device responds with its input data from 0...128 bytes.
• A change-of-state message is a transfer of data sent whenever a data
change occurs.
A user-configurable heartbeat rate allows devices to indicate proper
operation during intervals between data changes.
• A cyclic message is a transfer of data sent at a specific user-configurable
rate, such as every 50 ms.
In addition to I/O messaging, the scanner module also supports PCCC and
CIP explicit messaging, defined later in this manual.
IMPORTANT
Throughout this document, input and output are defined from
the controller’s point of view. Output is data sent from the
controller to a device. Input is data collected by the controller
from a device.