From: Tim Hubberstey
Organization: Marmot Engineering
X-Mailer: Mozilla 4.79 [en] (Windows NT 5.0; U)
Subject: Re: Q: Baud rate generation with 22V10
Date: Tue, 26 Nov 2002 21:56:14 GMT
NNTP-Posting-Date: Tue, 26 Nov 2002 14:56:14 MST
Jim Backus wrote:
> I need an adjustable baud rate generator to generate 1x clocks for
> synchronous data transmission. Baud rates of 19,200, 38,400 and 64,000
> are the ones I really need but thought it would be handy to have the
> full range of standard speeds from 9,600 up to 64,000. It seems that
> the old baud rate generator chips are no longer made - at least I've
> not found a manufacturer.
> Presumably the way to do it now is with a GAL or FPGA? The company I
> work for uses the 22V10, so using one or more of those would be
> convenient. I've never used one before so perhaps some of you good
> folks on this NG could give me some pointers as to how complex it
> would be, how many flip flops etc are accessible for this sort of
> application? Are there other devices that would be more suitable?
> Perhaps a single chip micro would be a better alternative?
A 22V10 has 10 flip-flops, up to 22 inputs (hence the 22) and up to 10
outputs (hence the 10), but not simultaneously. They are actually very
simple devices and a look at a data sheet is where you should start.
Whether or not one is suitable for your application is going to depend
on several factors:
- what input clock frequencies do you have available? Obviously, 10 bits
gives you a maximum divide ratio of 1024:1 so if your clock is faster
than 9.8 MHz, 9600 is out of reach.
- how are you going to select the output rate? If you're supplying
discrete digital inputs you *may* be OK but but a processor-accessible
register is way too complex for this part. There are a very limited
number of logic terms available in a 22V10 and there may not be
sufficient to support the programability you are looking for.
CPLDs are a better option if you are looking for more complex features
as they are cost-competitive with GALs but have a lot more
functionality. Free tools are available for development. An FPGA is
unnecessarily complex and costly for this application, unless you can
pack a lot of other board features into it.
Tim Hubberstey, P.Eng. . . . . . Hardware/Software Consulting Engineer
Marmot Engineering . . . . . . . VHDL, ASICs, FPGAs, embedded systems
Vancouver, BC, Canada . . . . . . . . . . . http://www.marmot-eng.com