Installation and Upgrade Guide

Publication 1757-IN510A-EN-P - October 2003
11-20 Performance and Capacity Specifications
I/O Performance and
Capacity Specifications
Every I/O device presents a load on the 1757-PLX52 system
performance by utilizing I/O network bandwidth and 1757-PLX52
memory and CPU resources.
Many of these constraints are measured in I/O Units, which is a
generic loading definition used to normalize the load among the many
different I/O devices and families supported.
Refer to Table 11.R I/O Unit Load Constraints on page 11-20 for the
I/O unit load assigned to various devices and modules. By following
these configuration constraints, you can prevent the 1757-PLX52 from
being overloaded and increase the ability for the 1757-PLX52 to
operate correctly.
Table 11.R I/O Unit Load Constraints
I/O Device or Module I/O Units
1 1756/1757 chassis mounted I/O Module 1
1 1794 FLEX I/O or 1797 FLEX EX rail mounted I/O Module 1
1 1757-SIM FTA 4
1 1788-CN2FF, Foundation Fieldbus Linking Device 1
1 1757-FIM, Fieldbus Interface Module 3
1 DHRIO Module 1
1 SST-PFB-CLX Profibus Module 2 (for 64 Unit/CPM Limit)
6 (for 24 Unit/CNB Limit)
1 1756-DNB, DeviceNet Interface Module 2
Table 11.S I/O Module Capacity
I/O Module and Fieldbus Capacity 50 ms CEE 5 ms CEE
Maximum Number of I/O Units per 1757-PLX52
Refer to Table 11.R I/O Unit Load Constraints on page 11-20 for I/O unit definitions.
64 12
(local 1757/1756 I/O only)
Maximum Number of Remote I/O Chassis + 1757-FIM-Only Chassis+Remote Mixed
Chassis + 1794/1797-ACNR15s (combined) per 1757-PLX52.
8 0
(local 1757/1756 I/O only)
Maximum Number of I/O units per Downlink 1756-CNB
Refer to Table 11.R I/O Unit Load Constraints on page 11-20 for I/O unit definitions.
64 scheduled
24 unscheduled
0
(local 1757/1756 I/O only)
Maximum number of Downlink 1756-CNB’s per Controller Chassis 4 0
(local I/O only)
Maximum number of DHRIO modules per 1757-PLX52 2 2 (local chassis only)
Serial Interface Module (TC-MUX021) related only 50ms CEE 5ms CEE
Maximum Number of Serial Interface Modules per 1757-PLX52 3 1
Maximum Number of FTA assemblies per Serial Interface Module (TC-MUX021)
• Each FTA connected counts as 4 I/O units in the 64 I/O units per 1757-PLX52 and
the 24 I/O units per 1756-CNB calculation above.
2 2