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From: JHB@jita.nospam.demon.co.uk (Jim Backus)
Subject: Re: Baud rate generation with 22V10
Date: Mon, 2 Dec 2002 20:02:33 +0000 (UTC)
NNTP-Posting-Date: Mon, 2 Dec 2002 20:02:33 +0000 (UTC)
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On Wed, 27 Nov 2002 21:57:43, "petrus bitbyter"
> "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?
> > TIA
> > --
> > Jim Backus OS/2 - smarter than the average operating system
> > bona fide replies to jimb(at)jita(dot)demon(dot)co(dot)uk
> > http://www.jita.demon.co.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
Pieter, Thanks - I've got an AVR dev kit so that would almost
certainly be the easiest way to go.
The 9600, 19200 etc are in one series, the 14400 etc in a second and
64000 in a third. A simple binary divider like the 4060 wouldn't do
the three different series.
The data link is synchronous with 1x clock which should make it
simpler. Might be able to persuade the AVR to do flag testing too.
(Synchronous flag = 01111110)
bona fide replies to jimb(at)jita(dot)demon(dot)co(dot)uk
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