Rockwell Automation 1756-L6x_L7x ControlLogix System User Manual User Manual
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140
Rockwell Automation Publication 1756-UM001O-EN-P - October 2014
Chapter 8
I/O Modules
Because of the increased performance that is provided by the 1756-CN2,
1756-CN2R, and 1756-CN2RXT modules, many of the considerations that
must be made with the 1756-CNB and 1756-CNBR modules are not applicable.
With the 1756-CN2, 1756-CN2R, and 1756-CN2RXT modules, you can add
I/O while online as long as you use reasonable RPI settings and remain within
the CPU limitations of the ControlNet module.
When adding to the I/O Configuration with 1756-CN2, 1756-CN2R, and
1756-CN2RXT modules, make these considerations:
•
Digital I/O modules can be added as rack-optimized connections if the
parent module is configured with rack-optimized connections.
•
Digital I/O modules can also be added as direct connections.
•
Analog I/O modules can be added only as direct connections.
•
Disable the Change of State (COS) feature on digital input modules
because it can cause inputs to be sent more quickly than the RPI.
•
If you plan to add large amounts of I/O to the ControlNet network,
dedicate one ControlNet network for I/O. For the dedicated ControlNet
network, verify that there is little or none of the following:
–
HMI traffic
–
MSG traffic
–
Programming workstations
9
15.00%
3.3
13.20%
4.0
7.00%
10.0
4.80%
20.0
3.20%
50.0
2.60%
100.0
10
15.60%
3.6
13.20%
4.0
7.50%
10.0
5.20%
20.0
3.40%
50.0
2.70%
100.0
11
16.40%
3.8
13.50%
4.0
8.20%
10.0
5.50%
20.0
3.50%
50.0
2.70%
100.0
12
17.00%
3.8
14.00%
4.0
8.80%
10.0
5.80%
20.0
3.70%
50.0
2.80%
100.0
13
17.80%
3.7
14.60%
4.0
9.30%
10.0
6.10%
20.0
3.80%
50.0
2.90%
100.0
14
18.50%
3.7
15.20%
4.0
9.90%
10.0
6.40%
20.0
4.00%
50.0
2.90%
100.0
15
19.40%
3.9
15.80%
4.0
10.50%
10.0
6.70%
20.0
4.10%
50.0
3.00%
100.0
(1) Example assumes that adequate unscheduled bandwidth is available.
(2) Approximate use of the central-processing unit (CPU) of the module in percent.
(3) The average Actual Packet Interval with 2000 samples (shown in ms).
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)
CPU %
(2)
Avg.
API
(3)
CPU %
(2)
Avg.
API
(3)
CPU %
(2)
Avg.
API
(3)
CPU %
(2)
Avg.
API
(3)
CPU %
(2)
Avg.
API
(3)
TIP
While you can add a new digital I/O module to an existing rack-
optimized connection, you cannot add rack-optimized connections
while online.