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From: "petrus bitbyter"
Subject: Re: Baud rate generation with 22V10
X-Newsreader: Microsoft Outlook Express 5.50.4807.1700
Date: Wed, 27 Nov 2002 21:57:43 GMT
NNTP-Posting-Date: Wed, 27 Nov 2002 22:57:43 MET
Organization: chello broadband
"Jim Backus" schreef in bericht
> 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?
> Jim Backus OS/2 - smarter than the average operating system
> bona fide replies to jimb(at)jita(dot)demon(dot)co(dot)uk
What's in a Baudrategenerator? The old ones had the electronics for an X-tal
oscillator (not the crystal itself), a prescaler and a lot of dividers that
produced a range of Baudrate clocks. The Motorola MC14411 comes to my mind.
It needed a 1.8?? MHz Xtal (which was divided by three somehow) and had
fourteen clock outputs. It could produce clocks from 75 Hz to 614kHz in four
overlapping ranges due to a programmable prescaler. It was not cheap.
It may be clear that a single 22V10, which contains only 10 flipflops cannot
perform a job like this. To fullfill your wishes you need at least two of
them and a separate X-tal oscillator.
Nowadays I would use a CD4060 and a 2,457MHz X-tal for simple cases. (I did
not check wether it produces the baudrates you require.) A better choice is
a small micro with an appropriate X-tal. The smallest and cheapest PIC
12F629 can produce up to eight (jumper) selectable clocks in the required
range. But it requires some skills and a minimal tooling.
You can, of course, use some other programmable logic device. But you still
need a stable clock i.e. an X-tal oscillator. Where I live a PIC16F629 is
much cheaper then a 22V10. Which also requires skills and tooling.
Keep in mind that the UART may need clock that is a multiple of Baudrate you
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