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PICList Thread
'Low power RTC chip with serial interface'
1996\11\17@063505 by Zemin Liu

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HI,

I have a project which needs a battery powered real-time clock (RTC) chip. The
chip should have a serial port that can be connected to a PIC16C54. Does any
one know where there is such kind of chip, its type and source? Any help is
greatly appriciated.

Z. Liu

1996\11\17@082849 by maud

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Zemin Liu wrote:
>
> HI,
>
> I have a project which needs a battery powered real-time clock (RTC) chip. The
>  chip should have a serial port that can be connected to a PIC16C54. Does any
>  one know where there is such kind of chip, its type and source? Any help is
>  greatly appriciated.
>
> Z. Liu

Zemin,

I suggest you have a look at the Dallas DS1302.  This is an 8-pin
animal, it has very low current requirements, and is relatively easy to
talk to using a '54.

For further information on the device, check out their web site at
http//http://www.dalsemi.com/.

Good luck

John

1996\11\17@160617 by Don McKenzie

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Zemin Liu wrote:
> I have a project which needs a battery powered real-time clock (RTC) chip. The
>  chip should have a serial port that can be connected to a PIC16C54. Does any
>  one know where there is such kind of chip, its type and source? Any help is
>  greatly appriciated.

http://www.labyrinth.net.au/~donmck/rtc.html
has pointers to PIC code examples and data sheets on the Panasonic
NJU6355 and Dallas 1202/1302 Real Time Clocks.

Don McKenzie spam_OUTdonmckTakeThisOuTspamlabyrinth.net.au
DonTronics Tullamarine, Australia
http://www.labyrinth.net.au/~donmck

SimmStick(tm) A PIC proto PCB the size of a 30 pin Simm Memory Module.
EASY PIC'n Beginners Guide to using PIC 16/17 MicroChip products.
MEL PicBasic Compiler. Programmers from 15 USD.  Pic-Axe(tm) A New Tool.

1996\11\18@002934 by tjaart

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Don McKenzie wrote:
>
> Zemin Liu wrote:
> > I have a project which needs a battery powered real-time clock (RTC) chip.
The
> >  chip should have a serial port that can be connected to a PIC16C54. Does
any
{Quote hidden}

Try Philips 8583. It's a IIC device. Works well.
--
Friendly Regards

Tjaart van der Walt
______________________________________________________________
|  Another sun-deprived R&D Engineer slaving away in a dungeon |
|WASP International GSM vehicle tracking and datacomm solutions|
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|______________________________________________________________|

1996\11\18@021446 by nigelg

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In message  <9611171134.AA21186spamKILLspamzsu.edu.cn> .....PICLISTKILLspamspam.....MITVMA.MIT.EDU writes:

> I have a project which needs a battery powered real-time clock (RTC) chip. The
>  chip should have a serial port that can be connected to a PIC16C54. Does any
>  one know where there is such kind of chip, its type and source? Any help is
>  greatly appriciated.

I'm currently developing a genlocked time display for video camera signals,
the clock chip I'm using is the Philips PCF8583P. This is an eight pin I2C
chip, and also includes 256 bytes of EEPROM which can be used for storage.

I've not got it hooked up to a PIC yet, but I've got it connected to my PC,
and with the power disconnected it consumes 2.4uA from a 2.4v nicad.

In the UK it's available from RS Components, or many other sources. It's also
used in a number of VCR's, in particular Grundig ones (with a battery, so the
clock is always running), and in a Sharp TV/VCR (with a capacitor, only gives
a limited backup).

Nigel.

       /--------------------------------------------------------------\
       | Nigel Goodwin   | Internet : EraseMEnigelgspam_OUTspamTakeThisOuTlpilsley.demon.co.uk     |
       | Lower Pilsley   | Web Page : http://www.lpilsley.demon.co.uk |
       | Chesterfield    |                                            |
       | England         |                                            |
       \--------------------------------------------------------------/

1996\11\18@132849 by Matthew Mucker

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At 07:34 PM 11/17/96 +0800, you wrote:
>HI,
>
>I have a project which needs a battery powered real-time clock (RTC) chip. The
> chip should have a serial port that can be connected to a PIC16C54. Does any
> one know where there is such kind of chip, its type and source? Any help is
> greatly appriciated.
>
>Z. Liu
>
Dallas Semi makes ALL KINDS of realt time clocks, with various features and
whatsits.  Many can be battery backed for 10 years with a lithium battery
(uh... I think... this is from memory).  Call Dallas and get a databook.

-Matt

1996\11\18@133917 by Shawn Ellis

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>>
>>I have a project which needs a battery powered real-time clock (RTC) chip. The
>> chip should have a serial port that can be connected to a PIC16C54. Does any
>> one know where there is such kind of chip, its type and source? Any help is
>> greatly appriciated.
>>
>>Z. Liu
>
Phillips semiconductor makes a low power clock/calendar chip with an I2C
interface, I;ve used this chip with great success backed-up with a lithium
battery.  Ask for Phillips' I2C data book/catalog.

1996\11\20@145451 by Juan Jose Abba

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I also have the need to keep a clock running using a minimum of battery
current, and I was planning to go mostly software for the clock, instead of
a dedicated chip.

my plan is
1>install a 32.768 KHz xtal to T1osc pins.   I am looking to the 16C74 but
other chips have same capability.
2>control the clock increments with a Timer one interrupt routine.
3>put the pic to sleep during the time was not processing data.
During this period the 32KHZ oscillator will remain working, providing an
interrupt and wake up of the PIC, every desired period of time , up to two
seconds, ( see microchip AN580).

the interrupt routine will be something like;


int mili_sec,sec,min,hour,day,month,clock_flag;
#INT_TIMER1
TIMER1_INT_HANDLER()
{

Timer_1_high = 0x80;  // one second interrupt periods
                     // this will be the adjustment to compensate
                     // for slow / fast xtals
if (++sec>=60)
{
sec =0;
if  (++min>=60)
   {
     min = 0;
     if (++hour>=24)
      {
      hour = 0;
      ++day;
      IF ((day>28)&&(month==2))    // requires more work for leap year

      day = 32;
          IF((day>30)&&(((month<8)&&(!BIT_TEST(month,0)))
          ||((month>7)&&(BIT_TEST(month,0)))) )
          day = 32;
             IF ( day >31)
              {
              day = 1;
                if (++month>12)
                month = 1;          // year update not included yet
               }
            }
         }
     }

              {
          clock_flag = true;   // clock_flag true will advise
                                // main routine to display clock
                               // , clear flag and set pic to sleep.
              }
}

appears to me that having the code space this approach should be cheaper
than a dedicated chip.
juan


{Quote hidden}

1996\11\22@053536 by John Payson

picon face
> my plan is
> 1>install a 32.768 KHz xtal to T1osc pins.   I am looking to the 16C74 but
> other chips have same capability.
> 2>control the clock increments with a Timer one interrupt routine.
> 3>put the pic to sleep during the time was not processing data.
> During this period the 32KHZ oscillator will remain working, providing an
> interrupt and wake up of the PIC, every desired period of time , up to two
> seconds, ( see microchip AN580).
>
> appears to me that having the code space this approach should be cheaper
> than a dedicated chip.

This approach has many advantages; among them: the potential ability to
use a cheap RC oscillator as your main CPU clock.  For applications that
will be periodically waking from sleep, an RC clock can be extremely des-
irable because unlike a crystal it can start up nearly instantly.

Unfortunately, according to Microchip's errata sheet for the 16C74, that
oscillator really isn't as useful as you'd like.  If memory serves...

[1] When the main oscillator is running, it can sometimes garble the
   oscillation of T1.

[2] When T1 is running, the part uses an excessive amount of power (which
   pretty much defeats the purpose of sleep mode).

If Microchip produced a chip which fixed these problems, added a gray-counter
to the UART (allowing much finer baud-rate control and rendering the BRGH
bug irrelevant), included a built-in programmable/nudgeable RC, and was nice
and cheap... well, I'd sure like 'em.

By gray counter, btw, I mean a counter which uses graycode step patterns in
a feedback circuit to allow fractional counting.  For not much more logic
than a self-reloading timer, you could have a counter which would output
2^K [K=0..6] pulses for every 256-N [N=0..127] put in.  Such a timer could
generate any baud rate within its range, within 1%; if its range needed to
be extended, a simple prescalar would suffice.  Given the combination of
such a baud-rate generator, a 32KHz crystal, and an RC oscillator, it would
be practical to have a device sleep while waiting for serial input and be
able to grab the first byte.  Would anyone else find such a device interest-
ing?

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