Using a PIC microcontroller to interface with a DS1302 real time clock - Page 4 - Electronic Circuits Projects Diagrams Free

ssylee · 9th January 2008, 07:22 AM

I'm not trying to make it a stopwatch. Once I set it, I'm probably setting it for good. Using it as a timestamp.

blueroomelectronics · 9th January 2008, 07:23 AM

Then set the seconds last, you can't simple turn a bit on. You have to write the whole byte.

Pommie · 9th January 2008, 07:36 AM

Isn't the best way to use burst mode then the registers all get updated at the same time - once the 8th register is written.

Or, write the seconds first. As long as the value written is not 59 then there is no chance of the minutes/hours etc. rolling over during the update.

Mike.

blueroomelectronics · 9th January 2008, 07:39 AM

The burst mode is the way to go, since SPI is very fast you can update the RTC in a fraction of a second.

ssylee · 9th January 2008, 08:18 AM

How much faster would the burst mode be compared to accessing the register contents one at a time?

Pommie · 9th January 2008, 08:44 AM

It's not that it is faster. Burst mode has the advantage that none of the registers are written until you write the eight one, therefore ensuring that a register can't rollover during the update.

Alternatively, writing the seconds register first with a value other than 0x59 will make sure that rollover can't happen during the update.

Mike.

ericgibbs · 9th January 2008, 08:53 AM

hi,
I downloaded the attached asm file from the web yesterday.
Recently got a couple of DS1307's, used the asm file as a quick test with a 16F628A, worked OK.

Time set/read is via RS232.

I will re-search the web so I can credit the author..

EDIT:
The full description is here:
http://pdfserv.maxim-ic.com/en/an/AN3921.pdf

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9th January 2008, 07:22 AM	(permalink)
ssylee	I'm not trying to make it a stopwatch. Once I set it, I'm probably setting it for good. Using it as a timestamp.

9th January 2008, 07:23 AM	(permalink)
blueroomelectronics	Then set the seconds last, you can't simple turn a bit on. You have to write the whole byte. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

9th January 2008, 07:36 AM	(permalink)
Pommie	Isn't the best way to use burst mode then the registers all get updated at the same time - once the 8th register is written. Or, write the seconds first. As long as the value written is not 59 then there is no chance of the minutes/hours etc. rolling over during the update. Mike.

9th January 2008, 07:39 AM	(permalink)
blueroomelectronics	The burst mode is the way to go, since SPI is very fast you can update the RTC in a fraction of a second. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

9th January 2008, 08:18 AM	(permalink)
ssylee	How much faster would the burst mode be compared to accessing the register contents one at a time?

9th January 2008, 08:44 AM	(permalink)
Pommie	It's not that it is faster. Burst mode has the advantage that none of the registers are written until you write the eight one, therefore ensuring that a register can't rollover during the update. Alternatively, writing the seconds register first with a value other than 0x59 will make sure that rollover can't happen during the update. Mike.

9th January 2008, 08:53 AM	(permalink)
ericgibbs	hi, I downloaded the attached asm file from the web yesterday. Recently got a couple of DS1307's, used the asm file as a quick test with a 16F628A, worked OK. Time set/read is via RS232. I will re-search the web so I can credit the author.. EDIT: The full description is here: http://pdfserv.maxim-ic.com/en/an/AN3921.pdf __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 7th July 2008 at 11:23 AM.