On Tue, 8 Jun 2004 20:35:12 -0400, "David Evennou" <de@data-masters.com> wrote:

>I found the thread dated April 1st 2004, in a Google Groups search for SPI
>RTC.
>
>Thanks,
>David
>
>"David Evennou" <de@data-masters.com> wrote in message
>news:40c6539d$1_2@newsfeed.slurp.net...
>> I am looking for a RTC Chip, maybe with SPI for communications with
>> 68HC908GP32. Any suggestions?
>>
>> TIA,
>> David
>>
>>
>

You could try Maxim's MAX6902. It is an SPI compatible RTC, with timekeeping current 
consumption of 400nA at 2V. It also operates from 2v -> 5.5V. However it comes in a 
TDFN form factor (3mm x 3mm x 0.8mm). 

Accidently flick it with the tweezers and it's gone.

However I understand that Maxim's delivery schedules leave something to be desired.
Sample deliveries are ok though. Today I received a MAX1811 Li+ charger ic about a 
week after I requested a sample.

rickman wrote:
> Depending on your battery current budget, MCUs may not be a good fit. 
> ...exception ... both designed to run
> from a watch battery at just 1 or 2 uA currents. 

What about the MSP430? I have one in an application that runs a 32KHz
watch xtal and wakes each second to count time, using an average current
of 0.7uA. The advantage of the MCU is that you can make it do things
when it wakes other than just increment the time.  My app wakes on NVRAM
IButton contact and records its time (32bit seconds or YYYYMMDDHHMMSS)
into the button - reliably! (CRCs, scratchpad readback, all the good
stuff).

Clifford Heath.

rickman wrote:
> Jim Granville wrote:
> 
>>>>>"David Evennou" <de@data-masters.com> wrote in message
>>>>>
>>>>>>I am looking for a RTC Chip, maybe with SPI for communications with
>>>>>>68HC908GP32. Any suggestions?
>>
>>Schwob wrote:
>> > hi,
>> >
>> > what about some small micros using them as RTC?  For example the
>> > LPC900 family offers a long timer that can count seconds on each
>> > device when clocked with 32 kHz. Either bit banging an SPI or some
>> > other little task can be done as well. The devices start way below a
>> > Dollar for an 8-pin SO-package.
>>
>>  Small uC are in the right price region, but nailing down the actual
>>Icc can be a challenge :)
>>  MSP430 looks low in OSC-only mode, but comes in higher than C8051Fxxx
>>when running from FLASH at 32KHz.
>>
>>eg Philips LPC9xx data mentions a < 100KHz osc option, but only the
>>LPC7xx data sheets show curves and numbers.
>>The 14 pin LPC9xx devices have SPI hardware, so would look ideal
>>as Smart-RTCs/Wdogs - has anyone set one up, and measured Icc/Vcc ?
>>
>>For mainstream full feature RTCs (but i2c) there is PCF8563 from
>>Philips, and for vanilla alternatives (more uC SW) see Dallas DS1371
>>(Osc + timer only).
> 
> 
> Another problem with using an MCU as an RTC is that when the MCU is
> communicating it typically draws heavier currents than when it is in
> clock mode.  This can drain a battery and it is a real PITA to design a
> circuit for dual power.  I have looked at this issues at length and
> using an actual RTC chip is much preferred if back up battery power is
> required.  

  RTCs also often have this problem, with some specing lower numbers
so that Ibat is not the same as Icc.
  Some RTC's I've seen are as high as 200uA on Icc.
  The C8051F series have quite low 'flash active' figures, of
9uA for CPU run at 32KHz/2.7V.
-jg

Jim Granville wrote:
> 
> >>>"David Evennou" <de@data-masters.com> wrote in message
> >>>>I am looking for a RTC Chip, maybe with SPI for communications with
> >>>>68HC908GP32. Any suggestions?
> Schwob wrote:
>  > hi,
>  >
>  > what about some small micros using them as RTC?  For example the
>  > LPC900 family offers a long timer that can count seconds on each
>  > device when clocked with 32 kHz. Either bit banging an SPI or some
>  > other little task can be done as well. The devices start way below a
>  > Dollar for an 8-pin SO-package.
> 
>   Small uC are in the right price region, but nailing down the actual
> Icc can be a challenge :)
>   MSP430 looks low in OSC-only mode, but comes in higher than C8051Fxxx
> when running from FLASH at 32KHz.
> 
> eg Philips LPC9xx data mentions a < 100KHz osc option, but only the
> LPC7xx data sheets show curves and numbers.
> The 14 pin LPC9xx devices have SPI hardware, so would look ideal
> as Smart-RTCs/Wdogs - has anyone set one up, and measured Icc/Vcc ?
> 
> For mainstream full feature RTCs (but i2c) there is PCF8563 from
> Philips, and for vanilla alternatives (more uC SW) see Dallas DS1371
> (Osc + timer only).

Another problem with using an MCU as an RTC is that when the MCU is
communicating it typically draws heavier currents than when it is in
clock mode.  This can drain a battery and it is a real PITA to design a
circuit for dual power.  I have looked at this issues at length and
using an actual RTC chip is much preferred if back up battery power is
required.  

-- 

Rick "rickman" Collins

rick.collins@XYarius.com
Ignore the reply address. To email me use the above address with the XY
removed.

Arius - A Signal Processing Solutions Company
Specializing in DSP and FPGA design      URL http://www.arius.com
4 King Ave                               301-682-7772 Voice
Frederick, MD 21701-3110                 301-682-7666 FAX

>>>"David Evennou" <de@data-masters.com> wrote in message
>>>>I am looking for a RTC Chip, maybe with SPI for communications with
>>>>68HC908GP32. Any suggestions?
Schwob wrote:
 > hi,
 >
 > what about some small micros using them as RTC?  For example the
 > LPC900 family offers a long timer that can count seconds on each
 > device when clocked with 32 kHz. Either bit banging an SPI or some
 > other little task can be done as well. The devices start way below a
 > Dollar for an 8-pin SO-package.

  Small uC are in the right price region, but nailing down the actual
Icc can be a challenge :)
  MSP430 looks low in OSC-only mode, but comes in higher than C8051Fxxx 
when running from FLASH at 32KHz.

eg Philips LPC9xx data mentions a < 100KHz osc option, but only the
LPC7xx data sheets show curves and numbers.
The 14 pin LPC9xx devices have SPI hardware, so would look ideal
as Smart-RTCs/Wdogs - has anyone set one up, and measured Icc/Vcc ?

For mainstream full feature RTCs (but i2c) there is PCF8563 from 
Philips, and for vanilla alternatives (more uC SW) see Dallas DS1371 
(Osc + timer only).
-jg

Hi David,

Some folks have suggested a uC with realtime clock. Here is a good one: 
MSP430. Has an internal clock and when shut down with only this RTC 
running it consumes just a few micro amps.

Regards, Joerg

http://www.analogconsultants.com

Schwob wrote:
> 
> hi,
> 
> what about some small micros using them as RTC?  For example the
> LPC900 family offers a long timer that can count seconds on each
> device when clocked with 32 kHz. Either bit banging an SPI or some
> other little task can be done as well. The devices start way below a
> Dollar for an 8-pin SO-package.
> 
> Cheers Schwob
 
Depending on your battery current budget, MCUs may not be a good fit. 
They normally use a lot more power than a standard RTC which is designed
to run from a watch battery for years, just like watches.  

One exception is the MARC4 (4 bitter) from Atmel and a line of 4 bit
MCUs from EM owned by Swatch (surpise!).  These are both designed to run
from a watch battery at just 1 or 2 uA currents. 

-- 

Rick "rickman" Collins

rick.collins@XYarius.com
Ignore the reply address. To email me use the above address with the XY
removed.

Arius - A Signal Processing Solutions Company
Specializing in DSP and FPGA design      URL http://www.arius.com
4 King Ave                               301-682-7772 Voice
Frederick, MD 21701-3110                 301-682-7666 FAX

hi,

what about some small micros using them as RTC?  For example the
LPC900 family offers a long timer that can count seconds on each
device when clocked with 32 kHz. Either bit banging an SPI or some
other little task can be done as well. The devices start way below a
Dollar for an 8-pin SO-package.

Cheers Schwob

"YB" <yvan@no_spam_ybdesign.fr> wrote in message news:<ca6dgt$q4l$1@news.tiscali.fr>...
> Hi,
> Be careful if you choose DS1305 !!!
> I'm waiting for 100 pcs since 1.5 months...
> 
> --
> 
> Yvan
> http://www.ybdesign.fr
> 
> 
> 
> 
> "David Evennou" <de@data-masters.com> a &#4294967295;crit dans le message de news:
> 40c65b7c_1@newsfeed.slurp.net...
> > I found the thread dated April 1st 2004, in a Google Groups search for SPI
> > RTC.
> >
> > Thanks,
> > David
> >
> > "David Evennou" <de@data-masters.com> wrote in message
> > news:40c6539d$1_2@newsfeed.slurp.net...
> > > I am looking for a RTC Chip, maybe with SPI for communications with
> > > 68HC908GP32. Any suggestions?
> > >
> > > TIA,
> > > David
> > >
> > >
> >
> >

Hi,
Be careful if you choose DS1305 !!!
I'm waiting for 100 pcs since 1.5 months...

--

Yvan
http://www.ybdesign.fr




"David Evennou" <de@data-masters.com> a &#4294967295;crit dans le message de news:
40c65b7c_1@newsfeed.slurp.net...
> I found the thread dated April 1st 2004, in a Google Groups search for SPI
> RTC.
>
> Thanks,
> David
>
> "David Evennou" <de@data-masters.com> wrote in message
> news:40c6539d$1_2@newsfeed.slurp.net...
> > I am looking for a RTC Chip, maybe with SPI for communications with
> > 68HC908GP32. Any suggestions?
> >
> > TIA,
> > David
> >
> >
>
>

I found the thread dated April 1st 2004, in a Google Groups search for SPI
RTC.

Thanks,
David

"David Evennou" <de@data-masters.com> wrote in message
news:40c6539d$1_2@newsfeed.slurp.net...
> I am looking for a RTC Chip, maybe with SPI for communications with
> 68HC908GP32. Any suggestions?
>
> TIA,
> David
>
>