Matching time conditions

[malc-c]

Thanks...

Although I now have an understanding of how the DS1307 is accessed and what the registers are... I'm still a long way from understanding a 300 + page data sheet on one of the more complex PICs !, and I must confess I'm still at a loss on how to use the 1307 to match a value in the code an in turn set a value of a variable.

I assume that each byte for each register (01H, 02H etc) is converted from binary into BCD (which I gather is 4bit type code format of binary)... or does pbp simply read each byte at each register.

I guess the simple answer is to wait until I receive the new chip with the alarm function and use that ?

[Melanie]

The I2CRead command will simply grab the content of each Register.

With the DS1307, you find that bit 7 in some of the registers is used for odd things. So, stripping that out, the first four bits (0-3) is the units digit (in binary), and bits 4-6 is the tens digit (in Binary). Which is why they fiendishly called it Binary Coded Decimal.

You've noticed it's in BCD. The first thing is to convert it to something that is useable. So I end up with a single variable that is HOURS, another variable for MINUTES etc. It's easier to have a single byte whose content varies from 0 (zero) to 59 representing MINUTES, because then you can perform math on it directly.

If your Alarm time is stored in the PIC (say your morning alarm at 07 Hours and 15 Minutes) it's a simple matter to compare if those two variables (say ALARMHour and ALARMMinute) match what you've read from the RTC (after converting from BCD). I tend to ignore seconds because unless you're polling better than once a second (or have a hardware interrupt on receipt of the SQUARE wave the RTC can output), or if your code is sloppy, you can easily miss one second.

If you're really clever, you can convert the Date and Time to JULIAN Date & Time, which gives you a single variable which holds a linear combination of Year, Month, Day, Hour, Minute and Second. Now this is great, because then you can simply add 3600 to advance an hour etc etc. There's another thread somewhere on this forum where I did just that with another DS series chip (albeit some years ago). This is the method I choose to use for things like Alarms with a DATE attached (eg Central Heating Timers), whereas Alarms with just TIME (such as your bedside radio's) usually comparing Hours and Minutes suffices.

[malc-c]

Mel,

Thanks for that explanation. I've been watching the US Masters on TV so it's just coming up to midnight here in the UK, so will look at your suggestion tomorrow after work.

If your Alarm time is stored in the PIC (say your morning alarm at 07 Hours and 15 Minutes) it's a simple matter to compare if those two variables (say ALARMHour and ALARMMinute) match what you've read from the RTC (after converting from BCD).

Which is basically what I'm after. I intend to have an ALARMHour1 and ALARMHour2 to set an on time and off time to monitor.

Thanks once again for the push to try and understand these data sheets. It's somewhat clearer now

[malc-c]

Help !

I'm struggling with the conversion bit, and would appreciate some assistance.

To keep things simple I'm going to restrict the alarm values to just hours, so I have one Alarm variable called AlarmH1 which I'm trying to match to the RTCHour.

The I2C statement is thus

	I2CRead SDApin,SCLpin,$D0,$00,[RTCSec,RTCMin,RTCHour,RTCWDay,RTCDay,RTCMonth,RTCYear,RTCCtrl]

I'll now post the part of the code I'm using for testing in it's current state (sorry it's somewhat messy)

	LCDOut $FE,$80
	If RTCHour.6=1 then
			' Work-Out 12 or 24 hour Display for Hours
		CounterA=(RTCHour>>4)&$01
		else
		CounterA=(RTCHour>>4)&$03
		endif
	CounterA=CounterA*10+(RTCHour&$0F)
	If RTCHour.6=1 then
			' Display Hours appropriately for 12 or 24 hour Mode 
		LCDOut #CounterA
		else
		LCDOut #CounterA Dig 1,#CounterA Dig 0
		endif
		
	LCDOut ":",#(RTCMin>>4)&$0F,#RTCMin&$0F,":"
	LCDOut #(RTCSec>>4)&$0F,#RTCSec&$0F," "
	LCDOut $FE, $D4,"value = ",  #RTCHour;dec CounterA ;Dig 1,#CounterA Dig 0

    alarmhour = 25
    if alarmhour = rtchour then
     alarmled=1
    endif

The LCD is used to display the time and date, with line 4 used to "debug" what's happening with whatever I choose to display, eg as you can see dig1 and 0 og CounterA, ascii value of RTCHour, even tried DEC RTCHour etc. In the above example the LCD gives an ascii value of 25 for RTCHour hence the value for alarmhour. I've also tried using something like if DEC alarmhour = DEC RTChour but that still fails...

Can someone (Mel ?) point me in the right direction on how I convert the value stored in the RTCHour register into some usable format (decimal say ) that I can use. I'm hoping to use a repeat of the set up routine to allow me to set the on hour and off hour, but that will come later. For now I just need to find the best way to match the value....

[Byte_Butcher]

I use these with a DS1302 to convert RTC minutes, hours, etc, to BCD minutes.

decminutes =(rtcmin>>4)*10+(rtcmin & $0F)  'convert BCD minutes into Decimal minutes       .

rtcmin=((decminutes DIG 1)<<4)+decminutes DIG 0 'convert Decimal back to BCD      .

steve

[Melanie]

DecimalHours=RTCHours>>4
DecimalHours=(DecimalHours&$03)*10
DecimalHours=DecimalHours+(RTCHours&$0F)

RTCHours is read from the DS1307. It is in BCD format.

The first line takes bits 4 thru 7 and loads them into Decimal Hours as bits 0 thru 3. These are the DECIMAL TENS DIGIT VALUE of the BCD HOURS (plus a couple of additional control bits).

If you notice from the Datasheet, only bits 4 and 5 are the BCD TENS DIGIT (which we have moved to bits 0 and 1 of variable DecimalHours. Since we only need those two bits, we exclude all others with the AND '&' operator, ANDing it with $03. The result of that operation we simply multiply by ten. We now have our TENS DIGIT value extracted.

The third line takes the lower four bits ONLY (by ANDing them with $0F) of the RTCHours variable (those four bits being the BCD UNITS VALUE) and we ADD them to our previously extracted TENS VALUE.

We now have a BYTE variable called DecimalHours which contains a value between 0-23 (assuming you are running a 24 hour clock). You can Output it to your LCD with the command...

LCDOUT #DecimalHours

If you wanted your alarm at say 7am you can now simply say...

AlarmHours=7
If AlarmHours=DecimalHours then goto SoundKlaxxon

[malc-c]

Steve,

Thanks for that, which I guess is similar to some of the code posted above.

This is the section of code based on your suggestion, and it too displays the value of AlarmH1 as 21 when the rtc is displaying 21 hrs, however the led on D7 fails to light (I've tested an the hardware works)

//    Alarmh1 =(rtchour>>4)*10+(rtchour & $0F)  
    alarmhour = 21
	
	LCDOut ":",#(RTCMin>>4)&$0F,#RTCMin&$0F,":"
	LCDOut #(RTCSec>>4)&$0F,#RTCSec&$0F," "
	LCDOut $FE, $D4,"value = ",  dec alarmh1

    if alarmhour = alarmh1 then
     PORTD.7=1
    endif

Welcome any comments... even if it's to point out the illogical of my logical coding.

[malc-c]

Mel, thanks for the post, which happened whilst I was typing mine.

It's not the displaying of the time I'm having a brain freeze on, it's working out how to do the comparison with another variable so that if the condition is true (ie the hour set ( between 0 and 23) matches the RTC hour) the LED can be made to light (or a value in another variable can be set)