Newsgroups: sci.electronics
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Question: 10,000 bit wide UART
Message-ID: <1989Feb21.174450.8770@utzoo.uucp>
Organization: U of Toronto Zoology
References: <10108@pasteur.Berkeley.EDU>
Date: Tue, 21 Feb 89 17:44:50 GMT

In article <10108@pasteur.Berkeley.EDU> atn@cory.Berkeley.EDU (Alan Nishioka) writes:
>    I am trying to build a digital data link, as an experiment, which uses
>variable length packets (from 1 to about 10,000 bits in length).
>
>    All of the UART's that I could find only work with up to 9 bit characters.
>
>    Are there any UART's which work with longer bit strings?

You don't want a UART at all.  The A in UART stands for "asynchronous",
which refers to the technique which sends start and stop bits for every
character of data to resynchronize receiver and transmitter.  If you want to
send a whole bunch of bits without start and stop bits, that's *synchronous*
transmission, so you want a USRT or USART (which does either).  These
come in various forms; there are lots of them about.  Note that you will
need pretty good clock generation, since the receiver clock has to match
the transmitter clock to within half a bit time over the time needed to
send 10,000 bits.  This means either carefully-aligned clocks or some
sort of transmission scheme that sends clock information with the data.
It may be less trouble to just send 10,000 bits as 1250 8-bit bytes
using a UART.  Apart from some inefficiency (20% of the bits on the wire
are start and stop bits), is there a reason why this isn't adequate?
-- 
The Earth is our mother;       |     Henry Spencer at U of Toronto Zoology
our nine months are up.        | uunet!attcan!utzoo!henry henry@zoo.toronto.edu