Rockwell Automation Publication 1756-UM001M-EN-P - February 2012 147
I/O Modules Chapter 8
This table demonstrates the performance factors of the 1756-CN2/B,
1756-CN2R/B, and 1756-CN2RXT modules when adding I/O online.
Because of the increased performance 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 already configured with rack-optimized connections.
• Digital I/O modules can also be added as direct connections.
Table 40 - 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)
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
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 module’s central-processing unit (CPU) in percent.
(3) The average Actual Packet Interval with 2000 samples (shown in ms).
While you can add a new digital I/O module to an existing rack-optimized
connection, you cannot add rack-optimized connections while online.
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