Issues on Shift Register in a Clockless UART

shashi22k@rediffmail.com (Shashi) wrote in message news:<7cdabebf.0404201535.de4bbe8@posting.google.com>...
> Hi,
> I'm doing a project in clockless uart..as u know that the primary
> function of uart is parallel to serial conversion while transmitting
> and serial to paralel conversion while receiving..I was wondering if
> someone could tell me as how can i do a parallel to serial conversion
> and vice versa without using a clock.
> 
> Thank You
> SHASHI


Say...  Do you mean an "asynchronous" UART?  You *do* have a system
clock available to the FPGA, right?  Something in the MHz range?

Peter Alfke wrote:

(in answer to a question about a clockless UART)

> Simple answer: You cannot. You can of course generate your own clock...

Someone I know used to have a paper tape reader that you would
pull the tape through by hand.  A row of phototransistors and LEDs
would sense the holes as they went by, including the row of clock
holes.

I had wondered about making a card reader using a similar design,
but there are no clock holes.  It would be necessary to either run
the card at a constant speed, or otherwise measure the speed or
position of the card.  A rubber wheel and phototransistor/LED
sensor to read its position should be enough.

Paper tape is self clocking but punched cards are not.

-- glen