Forums

Real Time Clock Hardware

Started by Tim Wescott April 30, 2007
I need to put a real-time clock on a board.  I haven't needed to know 
anything about the market for this for years, and I see that I'm way out 
of date.

I just need basic clock functionality that I can read and set under 
software control, I don't need any bells or whistles, and I don't care 
much about the format.

What I do care about is something that I can put on the board easily and 
will work reliably.

I could put a chip, caps, crystal and battery on the board.  I see the 
24-DIP sized chips that come with the flip-top, though, and they look 
like I could short-cut a number of production issues by using them.

Does anyone have any experience with these things?  Are the tops 
interchangeable, or do I have to use a TI top with a TI bottom, ditto 
for NXP, etc.?

Any other positive or negative relevant experience anyone wants to share?

Thanks.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott wrote:

> I need to put a real-time clock on a board.
Use DS1307 Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Vladimir Vassilevsky wrote:
> > > Tim Wescott wrote: > >> I need to put a real-time clock on a board. > > Use DS1307 >
Do Dallas parts have the same ongoing availability nightmare associated with them that Maxim parts do? -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott wrote:


>>> I need to put a real-time clock on a board. >> >> Use DS1307 >> > Do Dallas parts have the same ongoing availability nightmare associated > with them that Maxim parts do?
This one is about as common as MAX232, so it should not be a problem at all. VLV
On Mon, 30 Apr 2007 07:44:17 -0700, Tim Wescott <tim@seemywebsite.com>
wrote:

>I need to put a real-time clock on a board. I haven't needed to know >anything about the market for this for years, and I see that I'm way out >of date. > >I just need basic clock functionality that I can read and set under >software control, I don't need any bells or whistles, and I don't care >much about the format. > >What I do care about is something that I can put on the board easily and >will work reliably. > >I could put a chip, caps, crystal and battery on the board. I see the >24-DIP sized chips that come with the flip-top, though, and they look >like I could short-cut a number of production issues by using them. > >Does anyone have any experience with these things? Are the tops >interchangeable, or do I have to use a TI top with a TI bottom, ditto >for NXP, etc.? > >Any other positive or negative relevant experience anyone wants to share? > >Thanks.
Epsom has some dips with the crystal inside and all. Just add a lithium battery and you'll be good for 10 years, maybe 20. John
On Apr 30, 10:30 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Mon, 30 Apr 2007 07:44:17 -0700, Tim Wescott <t...@seemywebsite.com> > wrote: > > > > >I need to put a real-time clock on a board. I haven't needed to know > >anything about the market for this for years, and I see that I'm way out > >of date. > > >I just need basic clock functionality that I can read and set under > >software control, I don't need any bells or whistles, and I don't care > >much about the format. > > >What I do care about is something that I can put on the board easily and > >will work reliably. > > >I could put a chip, caps, crystal and battery on the board. I see the > >24-DIP sized chips that come with the flip-top, though, and they look > >like I could short-cut a number of production issues by using them. > > >Does anyone have any experience with these things? Are the tops > >interchangeable, or do I have to use a TI top with a TI bottom, ditto > >for NXP, etc.? > > >Any other positive or negative relevant experience anyone wants to share? > > >Thanks. > > Epsom has some dips with the crystal inside and all. Just add a > lithium battery and you'll be good for 10 years, maybe 20. > > John
Maxim has the DS3231/DS3232 parts with a temperature compensated crystal. I am using the DS3231 on one of my boards and have been pleased with it. You do pay for the integration, however. -Michael
On Apr 30, 10:44?am, Tim Wescott <t...@seemywebsite.com> wrote:

Hey Tim,

The DS1307 is a reliable choice and we use it here.
Very straightforward one-wire communication, very good accuracy,
etc...
Can run on a crystal (32 khz), or the expensive (and very accurate)
companion DS32KHz TCXO
Also, straightforward to hook a backup battery, etc..

Note: If using the high stab osc., tucked away in a non-obvious app
note somewhere is a caution to use a high value resistor between the
two parts to avoid excessive current drain when operating on a coin
cell.  Be sure to review if you choose the 1307.

One drawback is that the 1307 requires 5-volts.
If you have that avail, then no problem.

But if not, take a look at the DS32B35.  (DS32C35)
Maxim sent me a datasheet on this a while ago and I recall it looked
rather promising.
It should be in production by now??  We may switch to it.?

It was an "all-in-one" unit.  RTC, TCXO time base, Non-Volatile
memory, etc...
Which means even though it has the bells and whistles, it might negate
the need for hardware elsewhere.  Was even or better on pricing than
the 1307.  Comes in a SO-20 package.

FYI - sometimes 1307's in DIP's can get scarce (which I suspect is due
to RoHS?), but pretty soon that will likely be the case with all
things DIP.....?

-mpm


Tim Wescott wrote:
> I need to put a real-time clock on a board. I haven't needed to know > anything about the market for this for years, and I see that I'm way out > of date. > > I just need basic clock functionality that I can read and set under > software control, I don't need any bells or whistles, and I don't care > much about the format. > > What I do care about is something that I can put on the board easily and > will work reliably. > > I could put a chip, caps, crystal and battery on the board. I see the > 24-DIP sized chips that come with the flip-top, though, and they look > like I could short-cut a number of production issues by using them. > > Does anyone have any experience with these things? Are the tops > interchangeable, or do I have to use a TI top with a TI bottom, ditto > for NXP, etc.? > > Any other positive or negative relevant experience anyone wants to share?
If cost is an issue, look at the JRC NJU6350. Cheap as dirt, tiny and we've not had any issues with it.
On 30-Apr-2007, Tim Wescott <tim@seemywebsite.com> wrote:

> >> I need to put a real-time clock on a board. > > > > Use DS1307 > > > Do Dallas parts have the same ongoing availability nightmare associated > with them that Maxim parts do?
We started having a tough time getting Dallas parts within a year of the Maxim takeover. I don't use any Maxim parts whatsoever. -Hershel
Jim Stewart wrote:
> Tim Wescott wrote: >> I need to put a real-time clock on a board. I haven't needed to know >> anything about the market for this for years, and I see that I'm way >> out of date. >> >> I just need basic clock functionality that I can read and set under >> software control, I don't need any bells or whistles, and I don't care >> much about the format. >> >> What I do care about is something that I can put on the board easily >> and will work reliably. >> >> I could put a chip, caps, crystal and battery on the board. I see the >> 24-DIP sized chips that come with the flip-top, though, and they look >> like I could short-cut a number of production issues by using them. >> >> Does anyone have any experience with these things? Are the tops >> interchangeable, or do I have to use a TI top with a TI bottom, ditto >> for NXP, etc.? >> >> Any other positive or negative relevant experience anyone wants to share? > > If cost is an issue, look at the JRC NJU6350. > Cheap as dirt, tiny and we've not had any > issues with it. > >
Cost is an issue. With a projected 50/year volume, engineering cost trumps all. The less we have to mess with battery holders, crystal selection, operation at cold and hot, board layout and/or part selection difficulties -- the better. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html