Data Link I/O Response Time

Section 8-3

mum number of words (1,200 words) per time.

For example, if the total number of data link words is 5,000, the result will be as shown below.

5,000/1,200 = 2.5 (approx. 3)

Cycle time of PLC at node #7 (2+3)

The PLC cycle time when data link words exceed 12,000 using a CS/CJ- series Controller Link Unit with unit version 1.2 or later is calculated as fol- lows.

12,000 to 15,600 (approx.) words: 3

15,600 (approx.) to 20,000 words: 4

Noise may increase I/O delays.

Case 3

The following diagram illustrates the data flow that will produce the maximum data link I/O response time when the cycle time of the PLC at node #1 < the communications cycle time and the cycle time of the PLC at node #7 the communications cycle time.

Input

I/O refresh

Input device

 

Input ON delay

 

 

 

 

Data exchange

X

(1)

 

1 cycle

 

 

 

 

 

Program

 

PLC at node #1

 

 

 

X

(2)

 

 

 

 

 

A

Controller Link Unit

 

 

 

 

 

 

 

 

 

transmission processing

 

 

 

 

 

 

Data link transmission

 

 

Communications

(3)

X

Controller Link Unit

 

 

 

 

 

 

cycle time

 

 

transmission processing

 

 

Previous communications

 

 

 

 

cycle data

 

 

X (4)

 

 

 

 

 

 

 

 

PLC at node #7

 

 

Program

 

 

 

 

 

1 cycle

 

 

 

 

 

 

Output device

 

 

 

 

 

 

Output ON delay

 

 

Data link I/O response time

 

Output

 

 

 

 

 

 

There are four points shown in the diagram above where processing is delayed, increasing the data link I/O response time.

1,2,3... 1. The input arrives in the PLC just after I/O refreshing, causing a delay of up to one cycle before the input is read into the PLC.

2.At point A, data from the previous exchange is still being transferred, so new data cannot be exchanged, causing a delay of one communications cycle time. Furthermore, the data exchange then occurs just after the PLC at node #1 passes the token for the polling node, causing another delay of one communications cycle time before the data is transferred in data link processing.

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Omron CVM1-CLK21, CS1W-RPT01, CJ1W-CLK21-V1, C200HW-CLK21, CQM1H-CLK21, CS1W-CLK21-V1 operation manual 259