Publication 1769-UM009B-EN-P - May 2002
1-4 Overview
Communicating with Your
Slave Devices
The scanner communicates with devices via strobe, poll, change of
state, and/or cyclic I/O messages. It uses these messages to solicit data
from or deliver data to each device. Data received from the devices, or
input data, is organized by the scanner and made available to the
controller. Data sent from your controller, or output data, is organized
in the scanner and sent on to your devices.
• A strobe message is a multicast transfer of data (which is 64 bits
in length) sent by the scanner 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 does not support the strobe message.
• A poll message is a point-to-point transfer of data (0 to 128
bytes) sent by the scanner to the slave device. The poll message
also initiates a response from each poll slave. The slave device
responds with its input data (0 to 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 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.
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