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52 Siemens Simatic S7 Driver Online Help

Feature: Using Secondary Poll Rates

With the SI7 I/O driver, you can specify a secondary poll rate. The driver polls a

datablock at its secondary poll rate once its access time expires. The driver remains

polling at the secondary poll rate until there is another request for data from

FIX/iFIX.

Using this feature, you can enter a secondary poll rate that is longer than the primary

poll rate. This configuration lets you reduce CPU time and communication requests

to the process hardware, while ensuring that the datablock is always polled.

Feature: Phasing Poll Rates

Phasing staggers the times at which the I/O driver scans your datablocks. This feature

prevents overruns that may occur when the I/O driver cannot collect all the data at the

specified poll rate. Use phasing to maximize the efficiency of your driver.

How It Works

By specifying a phase, you delay the driver’s first attempt to read data from the

datablock. When the phase time expires, the driver resumes reading the datablock at

the specified primary or secondary poll rate. Make sure the phase you enter is shorter

than the primary or secondary poll rate of the datablock.

See Also

The SI7 I/O Driver Features | Using Primary and Secondary Poll Rates with Access

Time | Understanding Datablock Timing Properties: Rate, Phase, and Access Time |

Using Phasing with Poll Rates

Feature: Enabling or Disabling Individual Channels, Devices,

and Datablocks

You can enable or disable messaging to channels, devices, or datablocks at any time.

This is a very useful feature for debugging, maintenance, and for making preliminary

configurations.

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