Rockwell Automation 1753-DNSI DeviceNet Safety Scanner for GuardPLC Controllers - Manual (Page 18)

Publication 1753-UM002A-EN-P - July 2005
1-8 Before You Begin
Communication Rate
The safety scanner supports the following communication rates, but
does not support autobaud:
• 125 Kbps (default)
• 250 Kbps
• 500 Kbps
Physical Layout of the
DeviceNet Safety System Planning your system helps ensure that you can:
• meet safety times
• use memory and bandwidth efficiently
• fulfill device-specific requirements
• leave room for system expansion
Before configuring your 1753-DNSI scanner, you should be familiar
with each of the DeviceNet devices on your network. You should
know each device’s:
• system safety time requirements
• communication requirements
• I/O size
• frequency of message delivery
You must also understand and define which data elements can be
treated as safety and which as standard in your intended
configuration.
DeviceNet Safety I/O Performance Factors
Safety nodes have priority on a DeviceNet network, but the
performance of DeviceNet Safety I/O modules can be affected by the:
• baud rate of the network (Lower baud rates mean slower
transmissions and slower responses.)
• packet size for the various connections (Bigger packets may
result in fragmented messages and slower responses than
single-packet messages, but use fewer resources.)
• type and number of connections used (Using point-to-point
connections to make multiple connections to an input node uses
more resources than a multicast connection.)
• RPI of the devices (Lower RPIs consume more bandwidth but
lower system reaction time.)