Rockwell Automation Publication 1756-UM001O-EN-P - October 2014
139
I/O Modules
Chapter 8
•
Requested Packet Intervals (RPIs) faster than 25 ms for unscheduled
modules can overload the 1756-CNB or 1756-CNBR communication
module. To avoid the overload, make these considerations:
–
Use a NUT of 10 ms or more.
–
Keep the SMAX and UMAX values as small as possible.
•
If the module has a Real Time Sample (RTS), disable it or set it to a rate
that is greater than the RPI.
•
You can add I/O modules until you reach these limits:
–
75% of CPU utilization of the 1756-CNB or 1756-CNBR
communication module.
–
Plan for a CPU-use increase of 1…4% of the 1756-CNB or
1756-CNBR module for each I/O module you add, depending on the
RPI.
–
48 connections on the 1756-CNB or 1756-CNBR communication
module.
–
Less than 400,000 unscheduled bytes per second are displayed in
RSNetWorx for ControlNet software after the network has been
scheduled.
1756-CN2, 1756-CN2R, 1756-CN2RXT Modules
The use of 1756-CN2/B, 1756-CN2R/B, and 1756-CN2RXT modules
provides increased capacity for adding I/O while online compared to 1756-CNB
or 1756-CNBR modules. With this increased capacity, you can easily add I/O
and increase ControlNet connections that are used with less impact on the
overall system.
demonstrates the performance factors of the 1756-CN2/B,
1756-CN2R/B, and 1756-CN2RXT modules when adding I/O online.
Table 35 - 1756-CN2, 1756-CN2R, and 1756-CN2RXT Performance Example
(1)
No. of Direct
Analog I/O
Connections
Added Online
RPI = 2 ms
RPI = 4 ms
RPI = 10 ms
RPI = 20 ms
RPI = 50 ms
RPI = 100 ms
CPU %
(2)
Avg.
API
(3)
Avg.
API
CPU %
Avg.
API
Avg.
API
CPU %
Avg.
API
CPU %
Avg.
API
0
1.50%
N/A
1.50%
N/A
1.50%
N/A
1.50%
N/A
1.50%
N/A
1.50%
N/A
1
4.80%
2.0
3.70%
4.0
2.50%
10.0
2.30%
20.0
1.90%
50.0
1.70%
100.0
2
7.00%
2.0
5.00%
4.0
3.30%
10.0
2.70%
20.0
2.10%
50.0
1.90%
100.0
3
9.00%
2.0
6.10%
4.0
3.80%
10.0
3.00%
20.0
2.20%
50.0
2.00%
100.0
4
11.20%
2.2
7.40%
4.0
4.40%
10.0
3.40%
20.0
2.40%
50.0
2.10%
100.0
5
11.50%
3.3
8.70%
4.0
5.00%
10.0
3.70%
20.0
2.60%
50.0
2.20%
100.0
6
12.80%
3.3
9.70%
4.0
5.50%
10.0
4.00%
20.0
2.70%
50.0
2.30%
100.0
7
13.80%
3.4
10.80%
4.0
5.90%
10.0
4.30%
20.0
2.90%
50.0
2.30%
100.0
8
15.10%
3.4
11.90%
4.0
6.40%
10.0
4.50%
20.0
3.00%
50.0
2.50%
100.0
Summary of Contents for 1756-L63XT
Page 4: ...4 Rockwell Automation Publication 1756 UM001O EN P October 2014 Summary of Changes Notes...
Page 18: ...18 Rockwell Automation Publication 1756 UM001O EN P October 2014 Preface Notes...
Page 136: ...136 Rockwell Automation Publication 1756 UM001O EN P October 2014 Chapter 8 I O Modules...
Page 210: ...210 Rockwell Automation Publication 1756 UM001O EN P October 2014 Index Notes...
Page 211: ......
