System Throughput Considerations

Introduction

System throughput describes the quantity of data in bytes that the PLC can process in a single scan. A Quantum EIO system should be designed so that the PLC can scan all the data produced by the system in a single scan. If the quantity of data produced by the system is excessive, and scan time is configured to be:

periodic: There will be a data overrun, i.e., not all data will be included in a single scan.
cyclic: The time required by the PLC to complete the scan may be undesirably long.

This topic presents throughput data for devices on a remote I/O local rack, which you can use to calculate the throughput of your own application.

Local Rack Throughput Device Capacities

A local rack can contain the following maximum numbers of devices:

Device	Maximum per Rack
140CRP31200 Ethernet remote I/O head module	1
140 CRP 93• 00 legacy (S908) remote I/O head module	1
140NOC78000 Ethernet distributed I/O head module	6 (see note below)
140NOC78100 Ethernet control head module	1
140 NOE 771 •• Ethernet port communication module	6 (see note below)
140 NOC 771 •• EtherNet/IP communication module	6 (see note below)
140 NOM 2•2 00 Modbus Plus communication module	6 (see note below)
NOTE: A local rack contains one 140CRP31200 remote I/O head module and a maximum of five 140NOC78000 distributed I/O head modules or other type of communication modules. You can install only one 140NOC78100 control head module. While the 140 NOC 78• 00 modules are designed specifically for a Quantum EIO system, you can use 140 NOE 771 ••, 140 NOC 771 ••, and 140 NOM 2•2 00 modules to manage Ethernet distributed I/O and/or Modbus Plus systems. Only one 140 NOE 771 •• module may participate in the remote I/O network. Only a 140 NOE 771 •• module can be interlinked with a 140CRP31200 module on the local rack. Do not interlink a 140 NOC 771 •• module with the 140CRP31200 module on the local rack. 140 NOC 771 •• modules are supported only in standalone systems; they are not supported in Hot Standby systems.

Each 140CRP31200 remote I/O head module can contribute the following maximum throughput:

Data Type	Maximum Capacity
input data	22,000 bytes
output data	10,000 bytes
MSTR block data	8,192 bytes (8 blocks, each with 1,024 bytes)

Each 140 NOE 771 00 communications module can contribute the following maximum throughput:

Data Type	Maximum Capacity
input data	4,000 bytes (input data)
input data	6,144 bytes (6 MSTR blocks, 1,024 bytes per block)
output data	4,000 bytes (output data)
output data	6,144 bytes (6 Modbus messaging blocks, 1,024 bytes per block)

Sample Architecture

For example, a could include:

1 - CPU
1 - 140CRP31200 Ethernet remote I/O head module managing:
- input data (7200 bytes)
- output data (2800 bytes)
- 2 MSTR blocks (2000 bytes)
1 - 140NOC78000 Ethernet distributed I/O head module managing the following data for a management network:
- input data (1200 bytes)
- output data (800 bytes)
- 4 MSTR blocks (4000 bytes)
1 - 140NOC78100 control head module managing the following data for a control network:
- input data (600 bytes)
- output data (400 bytes)
- 16 MSTR blocks (16000 bytes)

Given this design, the minimum backplane throughput, or bytes exchanged during a scan, would be:

7200+2800+2000+1200+800+4000+600+400+16000 = 35000 bytes

In this example, the I/O exchange requires 35 ms at each scan. Determine the PLC scan time that is compatible with this transfer time.