Debugging a Hot Standby Application

Introduction

You can write an application for your Quantum Hot Standby system in almost the same manner as you would for any other Quantum PLC. This is because the Quantum Hot Standby system does not require the use of special function blocks or user actions to provide most redundant features. There are some important exceptions to this statement. See Restricted Functions

NOTE: When in this section we use the word Debug, it doesn’t mean Debug mode (which concerns the use of break point), it means that we are debugging the application with all other tools that Control Expert software provides.

Debug and Diagnostic

The following tables presents Debug and Diagnostic operations for Quantum Hot Standby PLCs:

Diagnostic		140 CPU 671 60	140 CPU 671 60S	140 CPU 672 6•	140 CPU 678 61
Diagnostic Function Block		Yes	Yes	Yes	Yes
Diagnostic Buffer		Yes	Yes	Yes	Yes
Diagnostic Buffer characteristics	Max buffer size	16KB	25KB	25KB	25KB
Diagnostic Buffer characteristics	Max errors	160	254	254	254
Breakpoint*		1 max	1 max	1 max	1 max
Step by step (Into, over, and out)		Yes	Yes	Yes	Yes
Variable animation		End of MAST Watch Point	End of MAST Watch Point	End of MAST Watch Point	End of MAST Watch Point
Link animation		Yes	Yes	Yes	Yes

* Use of breakpoints is forbidden on a functioning (redundant) Hot Standby system.

If the primary CPU is connected to a standby PLC, do not use breakpoints on a primary CPU as this can cause a switchover.

You can use a breakpoint if the standby CPU is not connected or stopped.

Debug the Control/Command of the Procedure

Debugging a Quantum Hot Standby application program is a two-stage process:

Debug the basic program operation on one of the Hot Standby PLCs running as a Standalone PLC. When you do this, all of the debug and diagnostic resources noted in the tables above are available.

NOTE: If a standalone Hot Standby controller is not available, put the Standby PLC into a Non Conf state and do this first stage of debugging on the Primary PLC.
Debug any redundancy-specific aspects of your program on a functioning (redundant) Hot Standby system that is not actively managing your process. When performing this second stage, the debug and diagnostic resources in the tables above are not available.

WARNING

UNINTENDED EQUIPMENT OPERATION

When debugging the redundancy-specific aspects of your application program:

Always debug your application on a fully functioning Hot Standby system.
Only conduct debugging on a Hot Standby system that is not actively managing your process.
Do not use the Control Expert debug and diagnostic features except as permitted by this manual.
Confirm that the interaction of the MAST task mode and duration with the Watchdog values meet the needs of your application.

Failure to follow these instructions can result in death, serious injury, or equipment damage.

When you are conducting the second stage of debugging, confirm that you initially connect to the PLC currently acting as Primary. The Standby PLC only executes section 0 of the MAST task of your application program.

Debug the First Section of the MAST task in Standby PLC

To debug the first section in the Standby PLC application, the following points have to be taken into account:

All the application data that comes from the Primary PLC are displayed in a Standby animation table.
Animation tables can be synchronized with watch points. This is the best way to animate data in synchronization with code execution. Refer to the EcoStruxure™ Control Expert, Program Languages and Structure, Reference Manual.

Debugging the Redundancy Part

Do not attempt to debug or otherwise verify the performance of an application intended for use in a Hot Standby system on a non-Hot Standby PLC. You must debug Hot Standby-related applications on a Hot Standby PLC.

Do not use the debug and diagnostic operations normally available for Quantum PLCs on a redundant Hot Standby system. The operations such as step-by-step and breakpoints halt program execution and eliminate the redundancy of the Hot Standby system.

NOTE: A Switchover is not generated when the Primary application stops on a breakpoint.

The debugging that can be accomplished once your application program is loaded onto a redundant Hot Standby system offers the following debugging features:

Static verification. Check that:
- application restrictions in this manual have been observed
- MAST task characteristics have been configured properly
Dynamic verification

After each PLC has been made live (application already transferred), check that the redundancy function is correctly performed in each PLC: the Status register bit %SW61.15 is equal to 1 and the bit %SW61.6 is equal to 0.

Once the Hot Standby PLCs have entered either the Primary or Standby operating modes, confirm that:

all application program sections of the MAST task are executed on the Primary PLC
only the first section of the MAST task is executed in the Standby PLC