Baud Rate

Baud rate is the signaling speed of a serial line, measured in symbols per second — and for simple UART links, one symbol is one bit, so the terms are used interchangeably. It sets how fast data moves between a computer and a device over a serial connection, and it must be configured identically on both ends. A mismatch does not produce a clean error; it produces garbled, unreadable characters, which makes a wrong baud rate one of the most common — and most confusing — stumbling blocks when first connecting to a board.

Common rates and the miner default

Serial links run at a ladder of standard rates: 9600, 19200, 38400, 57600, and 115200 baud are the ones you will meet in practice. The overwhelming default for ASIC miner control boards, routers, and modern embedded Linux devices is 115200 baud, almost always paired with 8 data bits, no parity, and 1 stop bit — written together as 115200 8N1. The console UART on an Antminer's Zynq-based control board follows exactly this convention. Older or simpler hardware sometimes defaults to 9600, and bootloaders occasionally use a different rate than the kernel they hand off to. If a console shows random symbols, a wrong baud rate is the first suspect: step through the standard rates until the boot text becomes legible.

Why there is no error message

A UART link carries no shared clock — each end times the bits independently, and the configured baud rate is that timing. The receiver detects a start bit's falling edge and then samples the line at intervals derived from its own configured rate. Set the rate wrong and every sample lands at the wrong instant, slicing the waveform into nonsense that still looks like valid framing often enough to print garbage rather than nothing. This is also why baud rates have tolerance limits: the two ends' clocks only need to agree within a few percent across a 10-bit frame, which is what lets cheap oscillators on both sides interoperate — and why a marginal or drifting oscillator can produce a console that works when cold and corrupts when hot, a genuinely evil fault to diagnose.

Why it matters for repair

When you reach a stuck miner through its console pads, matching the baud rate is the difference between reading exactly which boot stage failed and staring at noise. A control board that seems dead over the network is very often alive on serial, narrating its failure — NAND errors, a corrupt kernel, a missing filesystem — in plain text at 115200 8N1. The diagnostic flow is standard bench work: connect a USB-to-serial adapter at the board's logic level, open a terminal at 115200 8N1, power the board, and read the boot text alongside the kernel log. Legible-then-garbage output mid-boot usually means the software changed console settings, not that your adapter failed. Note that the UART channels carrying work to the hash chips run their own signalling rates, managed by the firmware and (on Zynq boards) FPGA logic — the 115200 convention is about the human-facing console, not the hashboard links.

Getting it right the first time

Three settings rule serial debugging: the baud rate, the 8N1 line discipline, and the logic level of the adapter. Fix all three before assuming a board is dead. Baud rate is the timing half of wiring up a serial console; the electrical line it governs is the UART itself. Master those three entries together and a silent, "bricked" control board becomes a device that will usually tell you, in its own words, what is wrong — the starting point of nearly every control-board repair.