Allen-Bradley devicenet modules in logix5000 control systems 사용자 설명서
Publication DNET-UM004A-EN-P - March 2004
Tune the Performance of a DeviceNet Network 11-3
I/O Parameters of Each Device
The type of connection (message) that you configure for a device
determines when data transfers between the device and the scanner.
determines when data transfers between the device and the scanner.
• Each device has a default connection type. This is a good
starting point.
• Some devices may not offer all connection (message) types.
The following table describes the different types of connections
(messages) that you can configure for a device.
(messages) that you can configure for a device.
Background Poll
The foreground to background poll ratio lets you adjust how often the
scanner polls certain devices for their data. In general, use the default
values. Change them only if you need to tune the performance of
your system.
scanner polls certain devices for their data. In general, use the default
values. Change them only if you need to tune the performance of
your system.
Connection (message) type:
Description:
cyclic
Data transfers at the period that you specify. The default range is 48 - 32,000 milliseconds.
change of state (COS)
Both the scanner and the device sends data whenever the data changes. You also specify a heartbeat
period for the connection.
period for the connection.
• If the data does not change within the heartbeat period, the scanner and/or device sends their
data at the end of the period.
• This lets both the scanner and device know that the other is still operational.
strobed
The scanner sends a single strobed request to solicit data from the strobed devices.
• The request is 64-bits long (1 bit for each node).
• In response to the request, each device that is configured for a strobed connection sends its
• In response to the request, each device that is configured for a strobed connection sends its
data (up to 8 bytes).
polled
A point-to-point data transfer that occurs every I/O scan or as a ratio of the I/O scan (background).
• At the specified poll rate (every scan or background), the scanner sends data to a polled device
(up to 255 bytes). The data is either output data for the device or a request for input data from
the device.
the device.
• If the polled device gets a request for input data, it sends its input data (up to 255 bytes).
Parameter:
Description:
Default setting:
poll rate
• Applies to a device with a polled connection
• Defines whether the scanner polls the device every I/O scan (foreground) or as a
• Defines whether the scanner polls the device every I/O scan (foreground) or as a
ratio of the I/O scan (background)
every scan
foreground to background
poll ratio
poll ratio
• Applies to devices with a polled connection that is configured for a background
poll rate.
• Determines how often the devices are polled.
• By default, the scanner performs background polls every scan (poll ratio = 1).
• By default, the scanner performs background polls every scan (poll ratio = 1).
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