RS232 Uart for Virtex-II Pro

miniuart project at

is a ready-to use uart which works very well. A more sophisticated one is in uart16550 project but with miniuart is enough for most applications.

Javier Castillo

If it is transmit only, the design is very simple: you need a shift register that gets reloaded every 10/11 bit times with the byte, and fixed start and stop bits. The shift enable for the shift register has to be at the correct timing for the baud rate. For that, you can use a DDFS, which is nothing more than an accumulator which adds a fixed increment to itself on each clock The msb of the accumulator is your baud clock: synchronous edge detect that to obtain a shift enable for the shift register and your bit counter. Here's a vhdl snippet:

--DDFS generates bit clock from 50M clock ddfs

I have recoded a xilinx reference of UART and tested it in VIRTEX II.The reference is in VHDL.And It can reach 115K when communication with PC. If you interested it, you can contact me at snipped-for-privacy@gmail.com.