Introduction
System throughput describes the quantity of data in bytes that the CPU can process in a single scan. Design your M580 system so that the CPU can scan 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 is a data overrun. (Not all data is included in a single scan.)
cyclic: The time required by the CPU to complete the scan may be undesirably long.
This topic presents throughput data for devices on an RIO local rack, which you can use to calculate the throughput of your own application.
Local Rack Throughput Device Capacities
This table shows the maximum number of devices per local rack:
Device |
Maximum per Rack |
|---|---|
M580 CPU with Ethernet I/O scanner service |
1 |
BMENOC0301/BMENOC0311 Ethernet communication module |
3(1) |
BMENOS0300 network option switch module |
4(1) |
BMENOC0321 control network module |
1 |
BMXEIA0100 AS-interface module |
4(2) |
BMXNOR0200 Ethernet communication module |
3(1, 2) |
BMXNOM0200 Modbus communication module |
4(1, 2) (see note below) |
(1) A local rack contains an M580 CPU with Ethernet I/O scanner service and a maximum of six communication modules, depending upon the CPU you choose. (Only three of these communication modules can be BMENOC0301/311 modules.) While the M580 CPUs and BMENOC0301/11 modules are designed specifically for a M580 system, you can use BMXEIA0100, BMXNOR0200, and BMXNOM0200 modules. For the number of devices per rack supported by BME•585040 and BME•586040 CPUs, refer to the CPU selection table. (2) Not supported in local racks in M580 Hot Standby systems. |
|
Each CPU with Ethernet I/O scanner service can contribute the following maximum capacity:
Data Type |
Maximum Capacity |
|---|---|
input data |
24,000 bytes |
output data |
24,000 bytes |
explicit exchange function block data |
up to 8,192 bytes (8 blocks, each with 1,024 bytes), depending on CPU model |
Each CPU with DIO scanner service can contribute the following maximum capacity:
Data Type |
Maximum Capacity |
|---|---|
input data |
up to 4,000 bytes, depnding on CPU model |
output data |
4,000 bytes |
explicit exchange function block data |
6,144 bytes (6 explicit exchange function blocks, 1,024 bytes per block) |
Sample Architecture
For example, a local rack could include a CPU with Ethernet I/O scanner service managing an RIO network with 10 drops and only one MAST task, and a DIO network with 20 distributed devices.
In this example, the I/O exchange requires 15 ms on each scan. Determine a CPU scan time that is compatible with this processing time.