User manual

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.