Safety CPLD Isolation in JTAG Chains to Block Field Reprogramming
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Solution Overview
Problem
The challenge is to prevent unauthorized reprogramming of safety components in programmable logic devices (CPLDs) used in hazardous equipment, such as computer-to-plate imaging devices, to ensure safety and prevent potential eye damage from leaked laser light during operation.
Innovation Solution
A method is implemented where a safety CPLD is isolated from the chain of other CPLDs using analog switches, allowing it to be programmed only at the manufacturing site by setting specific output pins to logical states that disconnect it from the programming interface, ensuring it cannot be reprogrammed in the field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If CPLD components are made programmable via JTAG interface, then ease of repair and field reprogramming is improved, but safety reliability deteriorates due to risk of unauthorized reprogramming
Solution Approach 1:
The system segments the CPLD components into two distinct groups: safety-critical CPLDs and non-safety CPLDs. Safety CPLDs are isolated from the JTAG interface using analog switches, while non-safety CPLDs remain accessible. This segmentation allows field reprogramming of non-safety components without compromising the integrity of safety components, resolving the contradiction between repairability and safety reliability.
Solution Approach 2:
Analog switches serve as intermediary components between the JTAG interface and the CPLD components. These switches are controlled by a controller that receives identification signals from the CPLDs. The intermediary mechanism selectively connects or disconnects safety CPLDs from programming access based on their safety-critical nature, enabling conditional programming access that maintains both safety and repairability.
2Adaptability or versatility
If all CPLD components are connected to JTAG interface, then programming versatility is improved, but safety security deteriorates due to potential unauthorized access
Solution Approach 1:
The system implements dynamic control of JTAG interface connectivity through analog switches that can change connection states based on operational conditions. During manufacturing, all CPLDs are accessible for programming. During field operation, the controller dynamically disconnects safety CPLDs from the JTAG interface while maintaining access to non-safety CPLDs. This dynamic adaptability resolves the contradiction between programming versatility and safety security.
Solution Approach 2:
Different connectivity qualities are assigned to different CPLD components based on their functional classification. Safety-critical CPLDs receive restricted connectivity (disconnected from JTAG in field operation), while non-safety CPLDs maintain full connectivity. This local differentiation of access rights allows the system to maintain overall programming versatility while protecting specific safety-critical components, resolving the contradiction between versatility and security.
3Reliability
If safety CPLD is isolated from JTAG interface, then safety reliability is improved, but ease of manufacture deteriorates due to additional isolation circuitry
Solution Approach 1:
The analog switches and controller serve multiple functions: they enable selective isolation of safety CPLDs, provide identification and classification of CPLD types, and manage JTAG interface connectivity dynamically. This multi-functionality reduces the need for separate dedicated isolation circuitry, thereby mitigating the increase in manufacturing complexity while maintaining safety reliability.
Solution Approach 2:
The isolation mechanism is merged with the existing JTAG interface architecture rather than being implemented as a separate parallel system. The analog switches are integrated into the signal path between the JTAG interface and CPLD components, and the controller is incorporated into the existing control architecture. This merging approach minimizes additional circuit board complexity while achieving the safety isolation objective.
Data Source
AI summary
A method for a singular programming a programmable component in an electronic circuit includes providing a plurality of programmable components connected between each other in an electronic chain arrangement; providing an interface adapted to connect the programmable components to an external controller wherein the controller is adapted to program the programmable components; isolating and programming a safety component by setting an output pin in the safety component to logical state zero at first power up of the electronic circuit and logical state zero causes input and output data lines from the interface to be connected just to the safety component; and setting the output pin in the safety component to logical state one wherein the logical state one causes input and output data lines from the interface to disconnect from the safety component and connect to the electronic chain of the plurality of programmable components excluding the safety component.