Optimizing Application Response Time

Overview

You can reduce the maximum application response time (ART) for your system, by employing these network design tips:

use only the minimally required number of remote I/O drops (•••CRA312•0 adapter modules)
use only the minimally required number of remote I/O input and output modules
place the remote I/O drops with the fastest communications capacity nearest to the local rack containing the remote I/O head

In addition, you can further reduce ART by including up to 10 executions of IU_EIO immediate update function blocks in your Control Expert logic.

Reducing the Number of Remote I/O Drops

When you reduce the number of remote I/O drops in your system, you also reduce:

the number of hops that a packet passes through from a remote I/O drop to the 140CRP31200 remote I/O head module in the local rack
the number of packets received by the 140CRP31200 module

By reducing these values, you also reduce the following elements of ART:

network input/output times
network input/output jitter
140CRP31200 input/output jitter
CPU scan time (the greatest savings)

Reducing the Number of Remote Input and Output Modules

When you reduce the number of remote I/O input and output modules, you thereby also reduce the size of the packet, which in turn reduces the following elements of ART:

network input/output time
network input/output jitter
•••CRA312•0 drop process time

Placing the Fastest Remote I/O Drops Nearest to the Local Rack

When you place the fastest remote I/O drops nearest to the local rack, you reduce the number of hops that a packet passes through from the remote I/O drop to the local rack. You also reduce the following elements of ART:

network input/output time
network input/output jitter

Using Immediate I/O Function Blocks in Program Logic

WARNING

UNINTENDED EQUIPMENT OPERATION

Do not use the IU_ERIO function block in Quantum Hot Standby installations.

Failure to follow these instructions can result in death, serious injury, or equipment damage.

Using up to 10 executions of immediate update I/O function blocks can result in faster processing of I/O data when executing program logic, because outputs using immediate update I/O blocks are processed immediately. As a result, the only ART elements that apply to the execution of these blocks are network input/output times.

NOTE:

The same benefit does not apply during end of scan delays.
It may be possible to add more than 10 executions of IU_EIO immediate update function blocks in your Control Expert logic, depending on your specific application.

To reduce the time required to execute program logic:

Place the immediate update I/O blocks in the application so that they are equally spaced and, therefore, will execute at a fixed rate in the CPU scan.
Using the custom RPI option, adjust the Input RPI (CRA to CRP) so that it is one-half the period of the fixed rate immediate update I/O blocks are executed.

NOTE: Before adjusting the CRA to CRP RPI parameter and implementing the IU_EIO function block, refer to the Ethernet remote I/O exchange mechanism in the Quantum EIO Remote I/O Modules Installation and Configuration Guide for a full understanding.

For example, consider the case of a remote I/O drop with a CPU scan time of 40 ms. In this case, you could place immediate update I/O blocks in the program logic so that one is executed every 10 ms. You can accomplish this by setting the custom RPI option to 5 ms. Execution would proceed as follows:

With the insertion and spacing of immediate update I/O blocks, the ART in the above example would be one-fourth of the original.