I've been trying to specify some surface mount crystals.  I have two on my
board, one a 4MHz and one 32.768 khz.

Now, the thru-hole 4 MHz crystals come in a pretty big can, the standard
HC-49U package.  The thru-hole 32 kHZ cryustal comes in a tiny little can
looking about half the size of a 1 uF Cap.

In surface mount, I have only been able to locate crystals in gargantuan
packages that look like HC-49's with saurface mount tabs on the bottom.  The
surface mount 32 khz crystal is actually *bigger* than the thru hole 32khz
crystal, by about 10X.  I am not used to buying surface mount parts that are
*bigger*  than thru-hole.   Kinda like a subcompact car longer than a
Caddilac.

What type of crystals do you folks use on surface mount projects, and how
small do they get?

--Lawrence



----- Original Message -----
From: "Rick C." <rixy@VISUALLINK.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, June 10, 2002 4:16 PM
Subject: Re: [PIC] - Serial Woes and Crystals


> 20 mhz resonators aren't accurate enough for standard serial baud rates.
Yes,
> you need 2 caps on the xtal and almost any of the ones Digikey sells will
work.
> The MAX232 doesn't have anything to do with your problem unless your
interface
> isn't inverting the logic or you have other circuit issues. I have a
bullet
> proof routine for bit banging if you need it. Only about 50 bytes of
> instructions to send and receive data.
> Rick
>
> Rex Byrns wrote:
>
> > You guys have been a great help, the picusart.zip and the other serial
> > routines have been great, but I am having ZERO luck getting them to
work.
> >
> > The bitbang method is a method is a variation on
> > http://www.piclist.com/techref/piclist/cheapic/alpha4m.asm .
> >
> > I used the formula from the code to get the timing right. I have only
tested
> > the send routine, and I tried using Hyperterminal in 'view data' mode.
I
> > also tried the mscomm control in VB6.  I get nothing with both.
> >
> > One of the problems is that I am using a 20mhz resonator on both chips
> > (16f84a & 16f628)
> > I would really like to get a bitbang routine to work with the 16f84 and
the
> > USART going on the 16f628. 4mhz is the fastest 'proven code' that I have
> > found.  I don't really know what I am doing wrong and would love to have
> > code that is proven, so I can rule out hardware issues.  I have seen
several
> > formulas for baudrate, my resonator seems to be off several milliseconds
> > (using Roman's on the dot 1 second routine).  Between these two margins
of
> > error, not counting my inexperience, I am stuck.
> >
> > Should I just go ahead and buy a couple MAX232? Like digikey #
296-1402-5-ND
> > ?
> > For only $1.30 for the TI brand it's not bad.
> >
> > I would also like to order a 20mhz crystal, but don't know which one. Do
I
> > need caps?
> >
> > Thanks again.
> >
> > --
> > http://www.piclist.com hint: To leave the PICList
> > mailto:piclist-unsubscribe-request@mitvma.mit.edu
>
> --
> http://www.piclist.com hint: To leave the PICList
> mailto:piclist-unsubscribe-request@mitvma.mit.edu
>
>

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