Access In A Redundant System With Redundant Extension Base Unit - Mitsubishi Electric MELSEC iQ-R Series User Manual

11.8
Access in a Redundant System with Redundant
Extension Base Unit
Access to the extension base unit in a redundant system with redundant extension base unit is limited to the control system.
When systems are switched, access from the new control system (old standby system) to the extension base unit becomes
enabled.
Connection status when the extension cable is redundant
The redundant extension cables between the extension base units are divided into active routes that have access to the
modules and inactive routes that do not have access to the modules. The connection status of the extension cables can be
checked in the following ways.
• SD1760 (extension cable connection status) and SD1761 (extension cable route information)
• CONNECT/ACTIVE LED of the redundant extension base unit
Cable error between the main base unit of the control system and extension level 1
When an extension cable error occurs between the main base unit of the control system and the extension base unit, a stop
error occurs in the CPU module of the control system, and system switching occurs. In this case, communication with the
extension base unit is performed by the new control system, but the communication route of extension level 1 and later is not
switched. In addition, the new control system detects a continuation error by the stop error of the new standby system.
Cable error between the main base unit of the standby system and extension level 1
When an extension cable error occurs between the main base unit of the standby system and the extension base unit, a
continuation error is detected in the CPU module of the control system, and a stop error is detected in the CPU module of the
standby system.
Extension cable errors between extension base units
■When the extension cable is redundant
When an error occurs in the extension cable on the active side between the redundant extension base units, a stop error
occurs in the CPU module of the control system, and system switching occurs. In this case, communication with the extension
base unit is performed by the new control system, and the communication route in the section where the extension cable error
occurred is switched from inactive to active. In addition, the new control system detects a continuation error by the extension
cable error.
■When the extension cable is not redundant
If an extension cable error occurs in the following sections, the extension base unit in the level immediately below the section
where the error occurred cannot be accessed.
• Section where only one extension cable is connected
• Section where only one extension cable is recognized as connected properly due to an extension cable error
Therefore, although a stop error occurs in the CPU module of the control system, and system switching occurs, a stop error
also occurs in the new control system. In this case, communication with the extension base unit is performed by the new
control system.
■When system switching is disabled
When an error occurs in the extension cable on the active side between the redundant extension base units where system
switching is disabled due to a stop error in the standby system, the CPU module of the control system detects a stop error, but
no system switching is performed, and communication with the extension base unit is also performed by the control system. In
addition, the communication route of extension level 1 and later, including the communication route in the section where the
extension cable error occurred, is not switched, and the extension base unit in the level immediately below the section where
the extension cable error occurred cannot be accessed.
11 BASIC CONCEPT OF REDUNDANT SYSTEM
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11.8 Access in a Redundant System with Redundant Extension Base Unit