Modbus Slave Addressing With Sensor-Gated Virtual Responses
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Solution Overview
Problem
Traditional Modbus networks experience latency issues and address collisions as the number of slave devices increases, limiting response times in large networked systems such as distribution warehouses.
Innovation Solution
Implementing a networked system where each slave device stores both a unique and a non-unique slave address, allowing it to respond only to the non-unique address if its associated sensor is active, thereby reducing the number of responses needed and mitigating address collisions through sensor-activated response gating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of slave devices is increased to expand network capacity, then the network can support more devices, but latency increases and address collisions occur more frequently
Solution Approach 1:
The patent segments the addressing space by introducing two types of addresses: actual slave addresses (unique identifiers) and virtual slave addresses (group identifiers). This segmentation allows the network to organize slaves into groups based on virtual addresses, enabling efficient grouping and reducing the impact of having many slaves on overall latency.
Solution Approach 2:
The patent implements sensor-activated response gating where slaves only respond to broadcast requests when their associated sensor is active. This partial action principle reduces the number of responses generated in normal operation, thereby reducing latency and collision probability while still maintaining the capability to respond when needed.
2Reliability
If traditional unique addressing is used for all slave devices, then each slave can be individually addressed, but address collisions occur and response times increase in large networks
Solution Approach 1:
The patent makes slave addresses multi-functional by implementing both actual and virtual address capabilities in each slave device. Slaves can be individually addressed using actual addresses when precision is needed, or grouped using virtual addresses for broadcast operations. This universality allows the same addressing mechanism to serve both individual and collective addressing needs, reducing overall response time while maintaining reliability.
3Loss of time
If sensor-activated response gating is implemented, then latency is reduced and network performance improves, but the system complexity increases
Solution Approach 1:
The patent introduces virtual slave addresses as intermediaries between the master controller and multiple slave devices. These virtual addresses act as mediators that enable broadcast requests to be efficiently routed to groups of slaves without requiring the master to manage individual actual addresses for each slave, thereby reducing latency while keeping the complexity manageable through standardized protocol extensions.
4Quantity of substance
If the number of slave devices is increased, then network capacity expands, but address collisions become more frequent
Solution Approach 1:
The patent segments the address space into actual addresses (for unique identification) and virtual addresses (for grouping). This segmentation reduces address collision frequency by allowing broadcast requests to use virtual addresses that are shared among groups of slaves, eliminating the need for unique address assignment in all communication scenarios and thereby reducing collisions in large networks.
Data Source
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AI summary
Apparatus and associated methods relate to a networked system having a master and multiple slaves, where each slave stores a unique (actual) slave address and a non-unique (virtual) slave address in memory, such that each slave is configured to respond to request messages addressed to the slave's non-unique slave address if a sensor device associated with the is in an active state when the slave receives the request message. In an illustrative example, the networked system may be a Fieldbus-style network (e.g., a network implementing the Modbus protocol). A sensor device may be a break-beam, capacitive touch, or push-button device, for example. An output indicator/ actuator may be associated with a sensor device to indicate the status of the sensor device to a user. A networked system implementing sensor-activated response gating may beneficially expand the number of slave devices on the network while achieving low latency response times.