<< >>

UART Overview

UART is one of the most basic asynchronous communication protocols. Also known as RS-232, it transmits bits serially at a mutually agreed speed without providing a clock. The speed is known as the baud rate, and is typically something like 9600 baud, 115200 baud, or 10 Mbaud.

The most important characteristics are the following:

  • The baud rate.
  • The number of start bits, typically 1, sometimes 1.5
  • The number of data bits, typically 7 or 8
  • Whether a parity bit is present, and if so whether it is even parity or odd parity
  • The number of stop bits, typically 1, sometimes 2.

UART Implementation Alternatives

Two UART components are included in this repository, each consisting of two modules (one for each of RX and TX), summarised below:

Component modules Data rate Memory Parity Bits Per Byte Stop Bits
Generic UART
module_uart_tx
module_uart_rx
 to 115.2K ~1K Even/Odd/None 5/6/7/8 1 or 2
to 115.2K ~1K Even/Odd/None 5/6/7/8 1 or 2
Simple UART
module_uart_fast_tx
module_uart_fast_tx
 10 Mbaud 0.25K None 8 1
10 Mbaud 0.25K None 8 1

Generic UART

This module is completely parameterisable at run time and will require a thread for each of RX and TX. Unlike the simple uart below, it can operate at the standard UART baud rates.

Simple UART

This module is a much simpler implementation of a UART that will require a whole thread for RX and deliver up to 10 Mbaud. TX could be called as a function, and hence share a thread with other functionality although this will affect the TX baud rate achieved,and this usage is not shown.

It is fixed to 8 bits, a single start bit, no parity, and a single stop bit. All of those parameters could be changed by altering the source code.

The baud rate is parameterisable, but has to be a whole division of 100 MHz. This may make it unsuitable for some applications requiring a very particular baud rate.

Note that the code is easy to understand; it comprises the example from the XC programming manual.

Other Uarts

For an implementation of multi-uart suitable for applications where more than one uart is required, the sc_multi_uart component may be a better choice.

UART (0v1)