Rockwell Automation 1769-SDN Compact I/O DeviceNet Scanner Module User Manual - Manual (Page 73)

Publication 1769-UM009E-EN-P - August 2009 73
Manually Configure the DeviceNet Network Chapter 5
Foreground to Background Poll Ratio
Devices set for polled behavior can be polled on every I/O scan (foreground)
or they can be polled less frequently (background). Setting a device for
foreground or background behavior is done when you configure each device
in the scanner’s input section.
Foreground/Background Polling Behavior
Module Defaults
Clicking Module Defaults sets Interscan Delay and Foreground to Background
Poll Ratio to the following values:
• Interscan Delay: 10 ms
• Foreground to Background Poll Ratio: 1
Slave Mode
Enable Slave mode only if you want to use this scanner module as a slave.
Clicking Enable Slave Mode opens this dialog.
Poll Ratio = 1
Poll Ratio = 2
Poll Ratio = 4
F
X
B
1
B
2
B
3
B
4
F
X
B
1
B
2
B
3
B
4
F
X
B
1
B
2
B
3
B
4
F
X
B
1
B
2
B
3
B
4
F
X
B
1
B
2
F
X
B
3
B
4
F
X
B
1
B
2
F
X
B
3
B
4
F
X
B
1
F
X
B
2
F
X
B
3
F
X
B
4
Each waveform shows polling frequency
for the given Foreground to Background
Poll Ratio.
Where:
F
X
= x foreground slave devices.
B
1
= 1st background slave device.
B
2
= 2nd background slave device.
B
3
= 3rd background slave device.
B
4
= 4th background slave device.