USB Keyboard Matrix Layout for N-Key Rollover Without Ghosting
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Solution Overview
Problem
USB keyboards are limited to sending signals for a maximum of six normal keys simultaneously due to standard regulations, leading to key ghosting issues, which conventional methods like firmware programs and diode connections can only partially address, restricting key combinations and efficiency.
Innovation Solution
The USB keyboard arrangement employs a modified firmware program that rearranges key bit maps to allow each key to send isolated signals, using multiple reports and bit maps to redefine key areas, preventing ghost key conditions by avoiding crosspoints in the matrix circuit, enabling simultaneous reporting of up to six normal keys without ghosting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If firmware program is used to detect and distinguish ghost key conditions, then ghost key detection capability is improved, but key input reliability deteriorates because inputs during ghost key condition are read as null
Solution Approach 1:
The patent converts the harmful ghost key condition into a beneficial feature by deliberately designing the matrix circuit to generate ghost key signals at specific crosspoints. These ghost key conditions are then used to encode additional key information, allowing more than six keys to be detected simultaneously. The harmful electrical interference is transformed into a useful signaling mechanism for expanding keyboard functionality.
2Reliability
If diodes are added to every key input end to obviate ghost key condition, then ghost key condition is eliminated, but manufacturing cost increases
Solution Approach 1:
The patent creates a virtual copy of the diode function through firmware processing. Instead of adding physical diodes to every key, the system uses software algorithms to simulate the one-way current blocking effect of diodes, thereby eliminating ghost key conditions without the associated manufacturing costs. The firmware replicates the protective function of physical diodes in a cost-effective manner.
3Adaptability or versatility
If USB keyboard sends eight bytes of keycodes according to standard regulation, then compatibility is improved, but key combination capability deteriorates because only six normal keys can be sent at a time
Solution Approach 1:
The patent adds a temporal dimension to key code transmission by using multiple report frames. Instead of attempting to transmit all key information in a single byte structure, the system distributes key information across multiple time-stamped report frames. This allows the keyboard to maintain standard USB compatibility while progressively reporting more than six key states through sequential report frames, effectively breaking the six-key limit through time-based expansion.
4Ease of operation
If keys are arranged in four-crosspoint-array to follow Qwerty layout, then ease of operation is improved, but ghost key condition is inevitably incurred
Solution Approach 1:
The patent applies different properties to different regions of the keyboard matrix. Specific crosspoints are designated as ghost key generation zones where ghost key conditions are intentionally allowed and utilized for encoding additional key information. Other regions maintain traditional key detection properties. This localized differentiation allows the keyboard to preserve the familiar Qwerty layout while converting ghost key problems into functional features in specific areas.
Data Source
AI summary
A USB keyboard arrangement having N-keys rollover and the method thereof mainly make use of rearranging a keycode of a firmware program of the USB keyboard through sets of bit maps to control each key thereon. After modifying a matrix, each key within a certain key-area can favorably avert from key ghosting existed in the matrix circuit. Therefore, when all keys in the key-area are concurrently pressed, isolated signals of the keys can be simultaneously sensed. While alternatively adjusting the firmware program through the above methods and adapting the methods to the prior art to split the keys in the key-area of the matrix from the crosspoints of key ghosting, the key-area of the USB keyboard can be provided with concomitantly sending isolated signals.