RTC chip or PIC?

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- 27th July 2009, 15:04
flotulopex

RTC chip or PIC?

Hello,

I was asking myself why one would prefer to use an particular RTC chip instead of using a PIC running a 32,768kHz crystal?

Unfortunately, I don't have such a crystal in my drawer and can't make any tests but is there anything "obvious" making a big difference I do not see?
- 27th July 2009, 15:18
mackrackit

I like RTC because of all of the built in stuff. Date, time, alarms etc. Save alot of programming and code space. Always running, check it when needed.
- 27th July 2009, 16:12
dhouston

Quote:

Originally Posted by flotulopex

... why one would prefer to use an particular RTC chip ...

I prefer the ST M41T81. In addition to macrackit's points, it survives power cycles (even recording the time power was lost), can generate a squarewave of several frequencies and battery life is >10 years. I suppose one could duplicate all that with a small PIC but there's no cost saving.
- 27th July 2009, 19:15
aratti

Quote:

I prefer the ST M41T81

Good product, unfortunatly sold only in 8-pin SOIC package.

Al.
- 28th July 2009, 10:15
flotulopex

How to trigger the "second" increment?

I have started some trials with a DS1307.

Since the smallest "common" change in RTC are seconds, I assume there is no use for the PIC to query constantly the RTC; every second should be enough.

How do I achieve this? I couldn't find a clue in either datasheets
http://www.datasheetcatalog.org/data...xim/DS1307.pdf
http://www.datasheetcatalog.org/data...onics/7529.pdf

Maybe, I should rather use a RTC chip with alarm such as a DS1678
http://datasheets.maxim-ic.com/en/ds/DS1678.pdf
- 28th July 2009, 11:18
mackrackit

Here is what I do with the DS1337. I have not used the one you have.
Setup:

Code:

SecReg CON $00 DS_SCL VAR PORTD.1 DS_SDA VAR PORTD.0 RTC CON %11010000 sec VAR BYTE ' seconds MINs VAR BYTE ' minutes hr VAR BYTE ' hours day VAR BYTE ' day date VAR BYTE ' date mon VAR BYTE ' month yr VAR BYTE ' year

Then when I want to read the RTC:

Code:

I2CRead DS_SDA, DS_SCL, RTC, SecReg, [sec,MINs,hr,day,date,mon,yr] PAUSE 100 Serout2 PORTC.6, 16572, [ "TIME ", HEX2 hr, ":", HEX2 MINs, ":", HEX2 sec,$d, $a] Serout2 PORTC.6, 16572, [ "DATE ", HEX2 mon,"-",HEX2 date,"-",HEX2 yr,$d, $a]

Maybe this can be adapted to yours.
- 28th July 2009, 13:18
sayzer

Here are two types:

RV-3029-C2 : Extremely Accurate RTC Module with embedded Xtal.

* Offers temperature compensated time (very high time-accuracy of ± 6ppm from -40°C to +85°C and ± 8ppm from -40°C to +125°C.)

* Integrated Temperature Sensor with digital-output and offers 8 Bytes
RAM and 2 Bytes EEPROM for customer's application.

Here is another one:
RTC-4553
• Built-in crystal unit.
• Builtin 30 x 4-bit S-RAM.
• Reference pulse output. (1024 Hz, 1/10 Hz)
etc.
- 28th July 2009, 19:24
flotulopex

Trigger the time (seconds) change

Thanks mackrackit,

My question was more about to understand how to trigger the time (seconds) change to start a display update or refresh.

I was thinking about putting the PIC in low-power mode until the next second change happens; how to achieve this the best way?

So is there any particular specification of RTC chips that will allow one to find a modell having, for example, a functionality setting a bit or a flag telling the second has changed?

BTW, here is the code (multiple sources - thanks to All of them) I work on now for my tests:

Code:

<html><head></head><body><pre><code>' PIC16F630 Fuses @ DEVICE BOD_OFF @ DEVICE CPD_OFF @ DEVICE PROTECT_OFF @ DEVICE MCLR_OFF @ DEVICE PWRT_OFF @ DEVICE WDT_OFF @ DEVICE INTRC_OSC_NOCLKOUT '------------------------------------------------------------------------------- ' Registers 76543210 WPUA = %00110000 'Weak Pull-up of PORTA for SCL and SDA on DS1307 INTCON = %00000000 'Interrupts OSCCAL = %01100000 'Oscillator Calibration when Internal RC set to 4MHz OPTION_REG = %10000000 'PORTA Pull-Ups/TMR0/Prescaler CMCON = %00000111 'Comparator Module is OFF TRISA = %00000000 'Set Input/Output PORTA = %00000000 'Ports High/Low TRISC = %00000000 'Set Input/Output PORTC = %00000000 'Ports High/Low '------------------------------------------------------------------------------- 'PORTA.0 = ICSP Data 'PORTA.1 = ICSP Clock 'PORTA.2 'PORTA.3 = MCLR 'PORTA.4 = SDA 'PORTA.5 = SCL 'PORTC.0 = LCD-DB4 'PORTC.1 = LCD-DB5 'PORTC.2 = LCD-DB6 'PORTC.3 = LCD-DB7 'PORTC.4 = LCD-E 'PORTC.5 = LCD-RS '------------------------------------------------------------------------------- ' LCD cabling '- ( 1) Vss - GND '- ( 2) Vdd / Vcc +5V '- ( 3) Vee / Vo / Contrast adjust / Pot 4k7(1-2-W3) or R2k2 (GND-3) 'PORTC.5 ( 4) RS '- ( 5) R/W -> to Vss 'PORTC.4 ( 6) E 'PORTC.0 (11) DB4 'PORTC.1 (12) DB5 'PORTC.2 (13) DB6 'PORTC.3 (14) DB7 DEFINE LCD_DREG PORTC 'LCD data port DEFINE LCD_DBIT 0 'LCD data starting PORT.bit (0 or 4) DEFINE LCD_RSREG PORTC 'LCD register select port DEFINE LCD_RSBIT 5 'LCD register select bit DEFINE LCD_EREG PORTC 'LCD enable port DEFINE LCD_EBIT 4 'LCD enable bit '------------------------------------------------------------------------------- ' Variables SDA VAR PORTA.4 'DS1307 SDA pin #5 SCL VAR PORTA.5 'DS1307 SCL pin #6 'SDOut var PORTC.2 DB VAR BYTE[8] 'Data byte array RTCSec VAR DB[0] 'alias individual bytes in array RTCMin VAR DB[1] RTCHour VAR DB[2] RTCDay VAR DB[3] RTCDate VAR DB[4] RTCMonth VAR DB[5] RTCYear VAR DB[6] RTCCtrl VAR DB[7] AMPM VAR BIT A_Ctr VAR BYTE 'counter B_Ctr VAR BYTE 'counter Day_T VAR BYTE Day VAR BYTE[3] Day[0] = 0 Day[1] = 0 Day[2] = 0 '------------------------------------------------------------------------------- PAUSE 1000 'time for LCD to settle LCDOUT $FE, 1 'Clear LCD GOSUB WRITE_1307 'set the time or don't MAIN: GOSUB READ_1307 'Read the time & date GOSUB LCD PAUSE 1000 GOTO MAIN: '------------------------------------------------------------------------------- LCD: 'Hour in "hh:mm:ss" LCDOUT $FE, 2, DEC (RTCHour>>4 & $0F), DEC(RTCHour & $0F),":", _ DEC((RTCMin>>4)& $0F), DEC(RTCMin & $0F),":", _ DEC((RTCSec>>4)& $0F), DEC(RTCSec & $0F) 'Day B_Ctr = 0 FOR A_Ctr = (((RTCDay & $07)-1)*3) TO (((RTCDay & $07)-1)*3)+2 LOOKUP A_Ctr,["SunMonTueWedThuFriSat"],Day_T Day[B_Ctr] = Day_T B_Ctr = B_Ctr + 1 NEXT A_Ctr LCDOUT $FE, 2, $FE, $C0, Day[0], Day[1], Day[2] 'Date in "mm-dd-yyyy" LCDOUT $FE, $C4, DEC((RTCDate>>4)& $03), DEC(RTCDate & $0F),"-", _ DEC((RTCMonth>>4)& $01), DEC(RTCMonth & $0F),"-", _ DEC(((RTCYear>>4)& $0F)*100),DEC(RTCYear & $0F) RETURN '------------------------------------------------------------------------------- READ_1307: ' Read order is in Secs,Mins,Hours,Day,Date,Month,Year,Control I2CREAD SDA,SCL,$D0,$00,[STR DB\8] ' Read string of 8 bytes from DS1307 RETURN '------------------------------------------------------------------------------- WRITE_1307: 'Set time & date to 23:59:55, Day 2, Date:Month:Year 27:08:2009 I2CWRITE SDA,SCL,$D0,$00,[$55,$59,$23,$02,$27,$08,$29,$90] ' Write to DS1307 RETURN ' Sec Min Hr Day D M Y Control END </code></pre></body> </html>
- 28th July 2009, 19:29
dhouston

Many output a square wave from (1Hz to 32kHz for the M41T81). You can monitor it. At 1Hz, a rising edge comes once per second.
- 28th July 2009, 19:30
dhouston

Quote:

Originally Posted by aratti

Good product, unfortunatly sold only in 8-pin SOIC package.

What package would you prefer?
- 28th July 2009, 19:37
Melanie

The DS1307 is good +/- a few minutes every year.

A CR2032 Battery lasts many years. We've been shipping these for about seven years and haven't needed to change a Battery yet.

Use I2CREAD and I2CWRITE... example...

I2CWrite SDA,SCL,I2CAddress,DataB,[DataA]

where...

I2CAddress=$D0 (the BYTE value address for the device)

DataB is the BYTE value address representing the Register you are writing (usually in the range $00-$07 - see DS1307 Datasheet for what each register contains)

and DataA is the BYTE value that you are putting into the Register.

4K7 pull-up's on SCL and SDA required... a lower value may be required if you have multiple devices on the Bus.

You I2CREAD any time you feel like it... once a second, ten times a second... how ever often you feel like it. Note that you can program the DS1307 to output a pulse every second... you can use that to synchronise your PIC to read and display, or display on interrupt...
- 28th July 2009, 19:38
mackrackit

I think the DS1337's alarm can be set for one second. Probably doing the same thing as Dave mentioned with his.
- 28th July 2009, 21:40
flotulopex

Voilà

Okay.

So I modified the code as this:

Code:

<html><head></head><body><pre><code>' PIC16F630 Fuses @ DEVICE WDT_ON '------------------------------------------------------------------------------- ' Registers 76543210 WPUA = %00110100 'Weak Pull-up of PORTA for SCL and SDA on DS1307 TRISA = %00000100 'Set Input/Output '------------------------------------------------------------------------------- ' Variables DSOut VAR PORTA.2 'DS1307 SQW pin #7 '------------------------------------------------------------------------------- MAIN: IF DSOut = 0 THEN GOSUB Read_1307 'Read the time & date GOSUB lcd 'put PIC in low-power mode for 576+288+72=936ms NAP 5 NAP 4 NAP 2 ENDIF GOTO MAIN: END </code></pre></body> </html>

Maybe it doesn't make a lot of sense to put the PIC in low-power mode. How is it done in the "industrial" life?
- 28th July 2009, 22:02
rmteo

Also, you can now get PIC's with a built-in RTCC. :)