Definition
UART (Universal Asynchronous Receiver/Transmitter) is a simple asynchronous serial interface that moves data over two signal wires — transmit (TX) and receive (RX) — plus a shared ground. On ASIC control boards the UART exposes the boot console: the live text stream from the bootloader and Linux kernel as the Zynq SoC powers up. For a repair technician it is the single most useful diagnostic port on the board.
Finding and using the header
The UART header is usually a 4-pin row near the SoC, silkscreened UART, J1, or DEBUG, with a common pin order of GND, TX, RX, VCC. You connect it to a PC using a USB-to-TTL serial adapter such as an FTDI FT232RL or CP2102 board, then open a terminal at the board's baud rate. Critically, leave the adapter's VCC pin disconnected if the board is already powered — you only need GND, TX, and RX.
What it reveals
The console shows exactly where a boot fails: a corrupted NAND image stalling the bootloader, a kernel panic, or a hashboard that never initializes. This makes UART the fastest way to tell a recoverable firmware problem from a dead control board. Many recovery procedures also drop you to a bootloader prompt over UART to reflash a clean image.
UART is one of several serial buses on the board; for the bus that reads hashboard EEPROMs, see I2C Bus.
In Simple Terms
UART (Universal Asynchronous Receiver/Transmitter) is a simple asynchronous serial interface that moves data over two signal wires — transmit (TX) and receive (RX) — plus…