Forums

Real Time Clock

Started by David Evennou June 8, 2004
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 > >
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 &#2013265929;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,

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 &#2013265929;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 > > > > > > > > > >
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 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
>>>"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
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
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
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.