PLC Memory Attribute Mapping for Power-Off Data Retention
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Solution Overview
Problem
Existing control devices for industrial machines, such as PLCs, require significant time and effort to modify programs when attributes of data units change, especially when switching between data held and not held during power off states, leading to inefficiencies and increased scan times.
Innovation Solution
A control device with a plurality of memories, including a non-volatile SRAM for holding data and a volatile DDR memory for not holding data, along with circuitry to set attributes and addresses for each data unit, allowing seamless switching between memories without modifying the control program, using virtual addresses to maintain series access even when physical addresses are not sequential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If data units are stored in different memory types based on hold attributes, then data management efficiency is improved, but program modification time increases
Solution Approach 1:
The memory system is segmented into multiple memory types (first memory for holding data, second memory for not holding data) based on the hold attribute of data units. This segmentation allows efficient data management by storing data in appropriate memory types, while the automatic address allocation ensures program modification time is minimized through virtual address mapping that abstracts the physical memory distribution.
Solution Approach 2:
A virtual address mapping mechanism acts as an intermediary between the control program and physical memory addresses. The setting circuitry automatically allocates virtual addresses that correspond to appropriate physical memory addresses based on hold attributes, eliminating the need for program modifications while maintaining efficient data storage management.
2Productivity
If multiple memory types are used for different data units, then data storage efficiency is improved, but device complexity increases
Solution Approach 1:
The control device performs self-service by automatically allocating virtual addresses to data units based on their hold attributes without requiring external intervention or program modification. The setting circuitry autonomously determines the appropriate memory type for each data unit and assigns corresponding virtual addresses, simplifying the user interface while maintaining efficient data storage management.
3Speed
If virtual addresses are used for memory access, then access speed is improved, but address management complexity increases
Solution Approach 1:
The virtual address system serves multiple functions: it provides fast memory access through direct mapping, automatically manages address allocation based on hold attributes, and abstracts the complexity of physical memory distribution from the control program. This universal address management mechanism improves access speed while eliminating the need for complex user-side address management.
Data Source
AI summary
A control device configured to control an industrial machine, the control device having: a plurality of memories including a first memory configured to hold data when a power supply is off and a second memory configured to inhibit data from being held when the power supply is off; and circuitry configured to: set, in each of a plurality of data units, an attribute indicating whether the data unit is to be held when the power supply is off; and set an address of each data unit such that each data unit is stored in one of the plurality of memories corresponding to the attribute.