Using Pic as a digital clock/timer. How accurate?

[rocky79]

Thanks guys for all the help and links. I found a chip that does all the hard work for me on top of that it is featured with 2 alarm settings.
http://pdfserv.maxim-ic.com/en/ds/DS3232.pdf

I will give it try and will see how it goes.
Thanks again

[SteveB]

I've used the clock only version of the chip (a temp. compensated oscilattor) and can attest to it's accuracy. It was hard to get a hold of at the time, though supply might be better now.

SteveB

[rocky79]

I've used the clock only version of the chip (a temp. compensated oscilattor) and can attest to it's accuracy. It was hard to get a hold of at the time, though supply might be better now.

SteveB

Hello Steve,
I am using the RTC DS3232 from dallas. you said you have used it before. Can you share your picbasic code? I am having trouble setting the time.
when i read the time and date. I get them all as 4.
Here is mine:
'Using the pic 16f630

include "modedefs.bas"
define OSCCAL_1k 1
CMCON=%0000011' Turn off comparator module


minutes var byte
hours var byte
day var byte
date var byte
month var byte
year var byte

reset Var PORTC.0

rtcyear var byte
rtcday var byte
rtcmonth var byte
rtcdate var byte
rtchour var byte
rtcmin var byte
rtcsec var byte

' Set initial time to 8:00:00AM 07/16/99
rtcyear = $99
rtcday = $06
rtcmonth = $07
rtcdate = $16
rtchour = $08
rtcmin =0
rtcsec =0

startbigNums con 2
endBigNums con 3
clrLCD CON 12
backLightOn con 14
backLightOff con 15
cursorPos con 16
enter con 10
bell con 7
b2 var byte
CONTL CON %01101000


Low reset 'reset the RTC
input reset ' undo reset..basically it puts pin reset at high impedance

'Set the time
I2cwrite PORTC.2,PORTC.1,CONTL,$01,[rtcmin] 'minutes
I2cwrite PORTC.2,PORTC.1,CONTL,$02,[rtchour]'hours
I2cwrite PORTC.2,PORTC.1,CONTL,$03,[rtcday] 'day
I2cwrite PORTC.2,PORTC.1,CONTL,$04,[rtcdate]'date
I2cwrite PORTC.2,PORTC.1,CONTL,$05,[rtcmonth]'month
I2cwrite PORTC.2,PORTC.1,CONTL,$06,[rtcyear] 'year


pause 10
'Low reset
'input reset
I2cread PORTC.2,PORTC.1,CONTL,$01,[minutes]
I2cread PORTC.2,PORTC.1,CONTL,$02,[hours]
I2cread PORTC.2,PORTC.1,CONTL,$03,[day]
I2cread PORTC.2,PORTC.1,CONTL,$04,[date]
I2cread PORTC.2,PORTC.1,CONTL,$05,[month]
I2cread PORTC.2,PORTC.1,CONTL,$06,[year]

serout2 0,16780,[clrLCD,"Time",hex hours,":",hex minutes,enter,_
"date:",hex date,"/",hex month,"/",hex year]
end

[SteveB]

Bad wording on my part. What I ment was that I have used one of the temperature compensated oscillators (the DS32kHz, not the DS3232 RTC) with other RTCs and as an input to the PIC timers, and they worked well. I'll have a glance at you code and the Datasheet to see if I can spot anything.

With other DSXXXX RTCs, I have seen the need to set some of the registers to appropriate setting before things work correctly. So that is one place to start.

I'll get back if I see anything.

SteveB

[BobK]

Hi Rocky,

I think your code is missing the clock register constants. I use the DS1337 RTC from Maxim. The code for this chip was posted here either in 2004 or 2005 by Tonigalea. This chip also has two alarms. The key to an accurate clock is as was mentioned before. But you must also use the correct crystal. The DS1337, for example, must have a crystal with a 12.5pf capacitance load. When you look in a parts catalog, DigiKey for example, look for the capacitance load for 32,768 crystals. They are around $.50 or less.

We also just covered RTC's with jcleaver using a DS1307. It looked like he also didn't list the RTC register constants. I sent him a copy of a program for that RTC and he got that going.

I would give a serious look at Paul Borgmeier's Easy Accurate Clock programs as they are very easy to work with and setting up user interface for alarms should be very easy also.

You asked a questions about the timing that no one seemed to answer. The PIC generates an internal time base which is derived from the Oscillator of the PIC divided by 4 so if you are using a 4mHz crystal then you PIC clock runs at 1mHz. Then there are programmable timers in the PIC that can be set up to count pulses then interrupt the PIC program to advance the clock program and/or do tasks at a specified time.

Hope this helps.

BobK

[rocky79]

Bob,
Can you specify what register constant i am missing? i look it up and i didn't see anything else i need to specify.Remember its the DS3232 i aim using so it might be slightly different than the other rtc's
Please let me know

thanks

[rocky79]

Bad wording on my part. What I ment was that I have used one of the temperature compensated oscillators (the DS32kHz, not the DS3232 RTC) with other RTCs and as an input to the PIC timers, and they worked well. I'll have a glance at you code and the Datasheet to see if I can spot anything.

With other DSXXXX RTCs, I have seen the need to set some of the registers to appropriate setting before things work correctly. So that is one place to start.

I'll get back if I see anything.

SteveB

Thanks steve! let me know if you find anything unusual or wrong i n my code...Thanks again

[BobK]

Hi Rocky,

Look on page 11 of the datasheet. The addresses in Hex and the register name under the function column are what you need. I have attached a listing example from a DS1337 program for an example. The datasheet had the same type of setup as this chip. You can't write any data to the RTC if it doesn't know where to put it.

Boy if I'm wrong here I really apologize but I think I'm right. Please let me know.

BobK

[rocky79]

Hi Rocky,

Look on page 11 of the datasheet. The addresses in Hex and the register name under the function column are what you need. I have attached a listing example from a DS1337 program for an example. The datasheet had the same type of setup as this chip. You can't write any data to the RTC if it doesn't know where to put it.

Boy if I'm wrong here I really apologize but I think I'm right. Please let me know.

BobK

Bob,

That's what i have on my code if you look back. Here is a sample take the minutes sample for example:
'Set the time
I2cwrite PORTC.2,PORTC.1,CONTL,$01,[rtcmin] 'minutes
the CONTL is the address of the RTC the $01 is the minutes register and the rtcmin is the value to be put in the register.
I hope you find my mistake.

Thanks