User manual

DeviceNet 5-2

Slave Device Communication

The BridgeWay continuously attempts to establish connections with devices con-

figured in the scan list (list of configured slaves). Once connections are estab-

lished, the module performs all necessary steps to configure the required I/O

messaging.

The BridgeWay provides explicit message proxy services for all group 2 only

slaves. Once any Group 2 only devices are configured, the BridgeWay sends

“keep alive” messages to the devices in addition to the I/O messages. This func-

tion prevents the explicit message connections between the BridgeWay and the

slave from timing out. This eliminates the need to re-establish an explicit connec-

tion should the BridgeWay need to send configuration data or serve as a proxy.

Scan Cycles

The BridgeWay employs a scan cycle for producing poll and strobe I/O messages.

A scan cycle consists of the following:

• A bit-strobe output message (if any devices in the scan list are configured

for bit-strobe).

• A poll command message for each device configured for polled I/O.

• A configurable delay before the next scan cycle.

The configurable delay is the Inter-Scan Delay (ISD). The ISD is a Scanner Con-

figuration Object attribute. The delay begins when the last poll command message

is transmitted and ends after the specified time has elapsed.

The BridgeWay also supports a background polling mechanism. A foreground to

background polling ratio can be specified to allow polling of devices at certain

scan cycle intervals.