Allen-Bradley devicenet modules in logix5000 control systems Manual Do Utilizador

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Publication DNET-UM004A-EN-P - March 2004

This chapter shows how to improve the performance of your 
network. As you configure and program your network, use the default 
settings whenever possible. Once your network is running, determine 
if you need to improve performance.

To improve the performance of your network, consider the following:

a specific device requires a faster update

Change the I/O parameters of the device to change of state 
(COS).

an analog device either:

• changes slower than the scan cycle
• requires a repeatable update period (e.g., for PID calculations)

Change the I/O parameters of the device to cyclic.

multiple devices are:

• input only

• I/O parameters are currently set to polled with an input size  

≤ 8 bytes

For each of those devices, change their I/O parameters to 
strobed.

2 or more devices send or receive large amounts of data (e.g., 
PanelView operator terminal)

1. For each of those devices, set their I/O parameters to 

polled with a poll rate = background.

2. For the scanner, set the poll ratio = 2. Increase the poll 

ratio if needed.

communication intermittently stops (status code 78) with a device that:

• sends or receives large amounts of data (e.g., PanelView 

operator terminal)
– and –

• has the I/O parameters currently set to polled

Increase the interscan delay.