LinkBo Protocol: Adaptive Single-Wire Communication

• LinkBo Protocol is an adaptive single-wire communication method that uses Manchester encoding and a 4-bit CRC to ensure robust, noise-resistant data transfer.
• It supports dual message formats, with high-priority messages offering minimal 50.4 μs latency for critical data and low-priority messages optimized for bulk transfers.
• Its FPGA-based hardware implementation enables reliable performance over distances up to 15 meters, making it ideal for real-time, embedded inter-chip communication.

LinkBo is an adaptive single-wire communication protocol developed to address latency, throughput, and robustness limitations inherent in existing single-wire inter-chip interfaces. Designed for variable-distance chip-to-chip communication—including extended PCB-level and inter-board links—the protocol delivers high-priority message latency as low as 50.4 μs and reliably supports wire lengths up to 15 meters at 300 kbps, achieving maximum data rates such as 7.5 Mbps for short connections. LinkBo’s specification includes Manchester encoding for improved synchronization and noise resilience, 4-bit cyclic redundancy check for error detection, and an integrated hardware-level interrupt mechanism to ensure timely delivery of critical data, surpassing commercial predecessors (1-wire, UNI/O) in both speed and robustness (Ye et al., 1 Sep 2025).

1. Protocol Structure, Message Types, and Encoding

LinkBo is realized as a peer-to-peer, single-wire protocol supporting two distinct message formats:

• High-Priority (HP) Messages: Each carries a single byte payload, utilizing a compact 15 Manchester bits format (2 sync bits + 8 data bits + 4 CRC bits + 1 ACK bit). HP messages deliver minimal latency (~50.4 μs), utilizing a unique sync field that forcibly sets the first bit slot low—this acts as a hardware interrupt, enabling the preemption of ongoing low-priority transmissions.
• Low-Priority (LP) Messages: Support variable payload size (1–7 bytes). LP messages incorporate a 3-bit size field with total length ranging between 18 and 66 Manchester bits. The design permits increased data throughput for bulk transfers with higher (but still bounded) latency, adjustable by payload and encoding parameters.

Manchester encoding (IEEE802.3 standard) is employed for all message types, ensuring self-clocking: the guaranteed mid-bit transition heightens synchronization margin and noise immunity. This approach contributes to LinkBo’s reliable operation over extended channel lengths.

2. Error Detection and Message Verification

Robustness in LinkBo is achieved by integrating a 4-bit cyclic redundancy check (CRC), computed using the generator polynomial $X^4 + X + 1$. Each transmitted message encloses the CRC field, verified on receipt:

$$P_{\text{crc}}(b) = \begin{cases} 1 & \text{if}\; b \leq 4 \ 1 - 1/2^4 & \text{if}\; b > 4 \end{cases}$$

where $P_{\text{crc}}(b)$ denotes detection probability for burst errors of length $b$, with $k=4$. This configuration yields 100% detection for bursts up to 4 bits, and 93.75% for longer bursts (Ye et al., 1 Sep 2025).

Acknowledgment (ACK) signaling uses a Manchester-coded single bit; only messages passing CRC validation are acknowledged, otherwise the absence of ACK signals transmission failure, prompting software or hardware-level retransmission.

3. Hardware Architecture and Implementation

The protocol has been physically implemented on FPGA platforms, using the following modular hardware blocks:

• Transmitter (TX): Employs finite state machines (FSMs), parallel-in/serial-out (PISO) shift registers, integrated CRC-4 generator (LFSR-based), and data stream multiplexers.
• Receiver (RX): Includes synchronization modules (detect falling edges of Manchester code), a prescaler counter (PSC) for bit slot measurement, Manchester decoder (for NRZ conversion), CRC divider, re-synchronization circuit, and a low-level detector (LBDET) to sense extended low pulses for HP interrupts.
• Driver: Features an XOR-based Manchester encoder, output multiplexer, and register, managing bus transitions and preventing signal hazards.
• Top-level module: Aggregates transmission, reception, synchronization, and message interruption orchestration, interfacing with a tri-state buffer and external pull-up to guarantee idle bus logic levels.

This hardware design enables protocol operation at clock frequencies up to 100 MHz (experiments typically used 3 MHz) and supports robust transmission over wire lengths up to 15 m.

4. Performance Metrics: Latency, Throughput, and Distance Dependence

Performance evaluation on FPGA testbeds demonstrates:

Metric	HP Message	LP Message (1–7 bytes)	Wire Lengths
Minimum latency	50.4 μs	60.6–224.4 μs	≤ 15 m for HP
Maximum data rate (short wire, 11 cm)	7.5 Mbps	up to 2.3 Mbps
Maintained throughput (5 m)	300 kbps (HP/LP)	300 kbps	up to 5.6 m (LP); 15 m (HP)

Latency remains effectively constant with wire length up to protocol-specified limits, after which throughput degrades predominantly due to signal integrity deterioration and parasitic effects. Cut-off frequency criteria for external RC filters were empirically set at $F_c = 3.3$ MHz, using $F_c = \frac{1}{2\pi RC}$ to maintain desired noise rejection without performance compromise.

Compared to existing single-wire protocols, LinkBo achieves at least 20× lower latency than the industry-standard 1-wire and 6.3× better than UNI/O for HP messages, alongside a marked improvement in throughput, reliability, and functional features (interrupt capability, ACK-on-error).

5. Interrupt-Driven Communication and Prioritization

LinkBo’s protocol-level interrupt mechanism enables immediate transmission of HP messages across the bus by generating a distinctive low sync pulse. This hardware feature preempts LP transfers, ensuring deterministic, bounded-latency delivery for time-critical or emergency signaling. Systems can thereby implement genuine real-time event notification, superior to protocols relying solely on software-polling or master-slave arbitration.

6. Practical Significance and System-Level Implications

The protocol's adaptive timing, physical-layer robustness, and compact message formats make LinkBo suitable for high-performance inter-chip communication on PCBs, board-to-board channels, and other embedded system contexts demanding minimized pin count and reliable variable-length links. Peer-to-peer scalability eliminates the single-point-of-failure risks typical of master-controlled arrangements, supporting resilient multi-device systems.

LinkBo’s error detection, fast interrupt response, and predictable latency profile substantiate its relevance to real-time control, fault-tolerant communication, and embedded systems requiring dynamic traffic prioritization. In practice, LinkBo offers substantive advancements in cost-effective, high-integrity digital interconnects for next-generation embedded hardware (Ye et al., 1 Sep 2025).