UART HWIP Technical Specification



This document specifies UART hardware IP functionality. This module conforms to the Comportable guideline for peripheral functionality. See that document for integration overview within the broader top level system.


  • 2-pin full duplex external interface
  • 8-bit data word, optional even or odd parity bit per byte
  • 1 stop bit
  • 64 x 8b RX buffer
  • 32 x 8b TX buffer
  • Programmable baud rate
  • Interrupt for transmit empty, receive overflow, frame error, parity error, break error, receive timeout


The UART module is a serial-to-parallel receive (RX) and parallel-to-serial (TX) full duplex design intended to communicate to an outside device, typically for basic terminal-style communication. It is programmed to run at a particular baud rate and contains only a transmit and receive signal to the outside world, i.e. no synchronizing clock. The programmable baud rate guarantees to be met up to 1Mbps.


The OpenTitan UART is feature compatible to a specific implementation in Chromium EC. Additional features such as parity have been added.