Configuring an M580 Hot Standby CPU

Introduction

This topic shows you how to configure the Hot Standby functionality of an M580 BMEH58•040 CPU. For information on how to configure the non-Hot Standby functions for the CPU, refer to the M580 Hardware Reference Manual.

NOTE: The same procedure, as described below, can also be applied to the configuration of an M580 BMEH58•040S safety CPU.

Accessing the M580 CPU Hot Standby Configuration Tab

Use the Hot Standby tab of an M580 BMEH58•040 CPU to configure its Hot Standby function. To access this tab:

Step	Action
1	Add a BMEH58•040 CPU to your project.
2	In the Project Browser, navigate to and select Configuration → PLC Bus → <rack> → <CPU>.
3	Click the right mouse button, then select Open.
4	Click the Hot Standby tab.

Configuring the Hot Standby Function

The Hot Standby tab presents the following configurable settings:

Setting		Description
Run Mode	Controller A Online	Specify if a PAC A and PAC B operates online at the next start-up: True (default): The PAC attempts to operate online at next start-up. Depending on the other conditions, the PAC may act as the primary or standby. False: The PAC transitions to either the Wait or Stop state at next start-up.
Run Mode	Controller B Online
Standby On Logic Mismatch	Number of modifications	The maximum number of online build changes from 1...50 that can be performed on the primary PAC. When this number of online build changes has been reached, you need to transfer the application from the primary to the standby to be able to make additional online build changes. Default = 20. NOTE: If this setting is set to 0, the Logic Mismatch Allowed flag has no effect. This setting cannot be edited via CCOTF.
Behavior of the CPU in Wait and Standby mode	CPU executes	Specify the sections of the MAST task the standby PAC executes in Wait state: All sections (default) First section No section at all When Control Expert is connected to the standby controller, all Sections in the Project Browser are preceded by: a green light for sections without condition or with a true condition even if not executed a red light for sections with a false condition NOTE: You can also individually specify the sections of the MAST task the standby CPU executes while in Wait state. Do this by adding a condition of execution in the Condition tab of the Properties window for a MAST task section. For a safety PAC, sections of the SAFE task are not executed when the PAC is in WAIT or STANDBY state. You can also individually specify the sections of the MAST task the standby CPU executes while in Wait state. Do this by adding a condition of execution in the Condition tab of the Properties window for a MAST task section.
Data Exchanged	–	A bar graph displays the percentage of CPU memory used by Hot Standby data. The value depends on the M580 Hot Standby configuration. The total data exchanged is displayed in KB as well as: data exchange by MAST data exchange by FAST data exchanged by SAFE (for a safety PAC)

Configuring Controller Online State

Controller A is the CPU with the A/B/Clear rotary selector switch (located on the back of the CPU) set to “A”. Controller B is the CPU with the A/B/Clear rotary selector switch set to “B”.

You can use the Controller A Online and Controller B Online settings, for the following purposes:

To specify the PAC that will be primary on a cold start. For example, set Controller A Online to True and Controller B Online to False. PAC A powers up as primary, and PAC B powers up in wait state. After power up, you can manually set Controller B Online to True.
To avoid an unintended switchover. For example, if PAC A is primary and PAC B is standby, set Controller B Online to False. PAC B enters wait state, and no switchover can occur.

These settings can be modified during runtime, or when the Hot Standby system is not operating.

Settings entered when the Hot Standby system is not running take effect after the next project build, when the Hot Standby system next starts-up.

If the Change Configuration on The Fly (CCOTF) function is enabled, settings entered when the Hot Standby system is running take effect immediately on the next project build (or re-build).

No Local I/O Configuration

Because the local rack of a Hot Standby PAC cannot include I/O modules, the following settings in a BMEH58•040 or BMEH58•040S CPU Configuration tab are disabled:

Run/Stop input
Run/Stop by input only
Memory protect
Maintenance Input (safety PAC)

NOTE: Instead of using the Run/Stop input, consider using the following approach to controlling the RUN/STOP operating state of a safety PAC:

Use a BMENOC0301 or BMENOC0311 communication module and the IPsec protocol to provide a secure connection to the CPU.
Then use the CMD_RUN_REMOTE or CMD_STOP_REMOTE commands of the T_M_ECPU_HSBY DDT to change a remote CPU operating state.

Enabling FDR Server Synchronization in a Hot Standby System

In an M580 Hot Standby system, a BMEH58•040 CPU, a BMENOC0311 CPU, or a BMENOC0301/11 Ethernet communication module can perform the role of an server. To permit the synchronization of the FDR server in the primary PAC with the FDR server in the standby PAC, you need to enable the service for the Hot Standby system.

To enable the TFTP service, follow these steps:

Step	Action
1	In the Project Browser double-click on the following: Project → Configuration → 0:PLC bus → <rack> → <CPU> → EIO. The RIO DIO Communicator Head window opens.
2	Click the Security tab.
3	For the TFTP service, select Enabled.
4	If Access Control is enabled, create an entry for each device or subnet that you want to have TFTP access to the CPU. NOTE: Select the TFTP column for each entry.
5	Validate and Save your edits.

NOTE: The FDR server cannot synchronize the primary and standby CPUs when the TFTP service is disabled. The TFTP service is enabled and disabled by the execution of the EthPort_Control_MX function in the application.

If you want to programmatically enable or disable TFTP, include the EthPort_Control_MX function in a section of the application that is executed by the standby CPU, so that this function will be executed by both the primary and standby CPUs.